referring now to the drawings , a preferred bileaflet heart valve prosthesis 110 of the present invention and parts thereof are illustrated . the bileaflet heart valve prosthesis 110 of the present invention is preferably fabricated from a metal such a titanium , a carbon compound ( or carbon with a minor percentage of silicon ) such as pyrolytic carbon or the like , a metal alloy , or a suitable substrate coated with pyrolytic carbon as are well known in the art . referring now to fig2 - 29 , a bileaflet heart valve 10 similar to the preferred heart valve prosthesis 110 of the present invention is shown diagrammatically implanted within the heart 101 of a patient , with the valve 10 sutured in place proximate to the mitral annulus 103 of the anatomical coronary valve and disposed above the papillary muscle and tendineae chordae 105 fixed to the posterior mitral annulus as described previously . the bileaflet valve 10 may be implanted in either the fully anatomical orientation or the fully anti - anatomical orientation as shown in fig2 and 27 , respectively , or adjusted between the fully anatomical and anti - anatomical orientations by rotating the valve 10 within the corresponding suture ring ( not shown ) as is well known to the art . these orientations may be compared with the anterior and posterior orientations of a monoleaflet valve m shown in fig2 and 28 . referring now to fig1 - 5 , a preferred embodiment of the bileaflet heart valve prosthesis 110 is described . the preferred bileaflet heart valve 110 of the present invention shown in fig1 includes an annular base 112 and first and second leaflets 114 . the fist and second leaflets 114 are mounted within the annular base 112 for pivotal movement between a fully open position , shown in fig1 - 5 and diagrammatically in fig1 , and in phantom in fig1 , and in a fully closed position shown in fig2 - 23 and diagrammatically in fig1 . referring now also to fig6 , the annular base 112 has a top surface 124 and an inner wall 126 which defines a generally circular bore 116 passing through the annular base 112 in a direction generally parallel with a longitudinal axis 128 oriented generally in parallel with a vertical path for circulation of fluid or blood through the generally circular bore 116 . the top surface 124 of the annular base 112 is raised proximate opposing lateral sides 129 . on the inner wall 2 inner surface sidewall 126 of the annular base 112 proximate the opposing lateral sides 129 , are flat portions 130 of lateral surfaces 133 which define flat lateral sides of the generally circular bore 116 . the flat portions 130 of the lateral surfaces 133 include a pair of recesses 132 in each of the respective lateral sides 129 of the base 112 . further lateral depressions 135 are centrally located in a lower portion of the inner surface 126 proximate each of the two lateral sides 129 , below and between the respective recesses 132 on each side , in the respective flat portions . in preferred embodiments , these depressions have a curvilinear surface which would define a portion of one side of a cone . the recesses 132 extend into the respective flat portions 130 of the lateral surfaces 133 , thereby displacing a cylindrical bottom surface 140 of the recess 132 from the respective lateral surface 133 proximate the respective lateral side 129 . in preferred embodiments of the present invention , each of the cylindrical bottom surfaces 140 of the respective recesses 132 pass through a cylindrical radius which is “ feathered out ” as the cylindrical surface 140 approaches a junction with the respective lateral surface 133 . referring now also to fig1 - 21 , a line 181 , shown in fig1 , which is tangential with a point on the cylindrical bottom surface 140 of the recess 132 just prior to a further point at which the cylindrical surface 140 is “ feathered out ” to form a junction with the lateral surface 133 , lies at an angle “ g ′” to a tangent line 184 which intersects line 181 and is tangential to the lateral surface 133 . in order to properly measure the entrance angle “ g ′” to the recess 132 , a number of lines similar to line 181 which are tangential to a point on the cylindrical surface 140 must be considered . this may be an infinite number of lines . the entrance angle , “ g ′”, will be the angle between the lines 184 and 181 which will be the greatest angle that exists between the line 184 and any of the lines which can be drawn which intersect with line 184 and are tangential to a point on the cylindrical surface 140 . this angle “ g ′”, is representative of a recess entrance angle to the cylindrical recess 132 . in preferred embodiments the recess entrance angle is less than about 35 °. preferably , the recess entrance angle “ g ′” is between about 20 ° and about 35 °. more preferably , the recess entrance angle “ g ′” is from about 25 ° to about 34 °. in even more preferred embodiments , the recess entrance angle “ g ′” ranges from about 28 ° to about 33 . 5 °. there is no preferred angle because the preferred angle may vary in response to changes in other parameters , especially the diameter of the annular base 112 . it will be appreciated that recesses to retain pivotal leaflets have existed in the bileaflet heart valve prostheses of the prior art for some time . it is believed , however , that a lower recess entrance angle will facilitate washing of the recess to minimize stagnation and potential for thrombogenic events in proximity to the recess 132 . therefore , it is believed that diminishing the angle of entrance to the recess 132 will provide for better washing activity and lessen any potential for embolism which may exist in patients utilizing prosthetic heart valves . referring now also to fig9 - 15 , the leaflets 114 have two sides , a top planar surface 142 and a beveled bottom side 143 . the bottom surface 143 has a peripheral bevel portion 144 proximate the peripheral edge 150 and a central portion or central bevel 145 proximate a mating edge 148 . the mating edge 148 has a narrow planar surface running nearly the entire width of the leaflet 114 . the respective leaflets are mirror images of one another in preferred embodiments so that when the respective leaflets 114 pivot to reside in the fully closed position , the mating edges 148 of the respective leaflets mate together to significantly obstruct blood flow through the very limited space between the respective mating surfaces 148 . it will be appreciated that some blood will “ regurgitate ” between the mating edges 148 of the respective leaflets 114 when they are closed . however , this is to be expected . in fact , such blood flow , while it should be minimized , performs an important function of cleansing the mating edges 148 as the blood regurgitates between the respective edges 148 . the central beveled portion 145 of the beveled bottom side includes a flat planar surface 146 which is flanked on either side along the width w of the leaflets 114 , by curvilinear side surfaces 147 a and 147 b which rise up proximate lateral sides 151 of the leaflets 114 to flat side bevels 147 c and 147 d which separate the mating edges 148 from the peripheral bevel 144 on the beveled bottom side 143 proximate the respective lateral sides 151 . the width wps of the flat planar surface 146 is greater than one - half of the width w of the leaflet 114 , and is therefore a major portion of the central bevel 145 . as used herein , the phrase “ a major portion ” means a portion of the whole which has a width dimension which is at least as great as that of one - half of the width of the whole . the respective lateral sides 151 of the respective leaflets 114 each have a cylindrical surface proximate the diamond - shaped cylindrical surface 154 . notches 153 , 155 are located adjacent to the diamond - shaped cylindrical surface 154 . the inflow notches 153 are located generally between the diamond - shaped cylindrical surface 154 and the top edge of the leaflet 114 . the generally v - shaped notch 153 is created and defined by an inflow flat 160 and an inflow side wall 156 of the diamond - shaped cylindrical surface 154 . the generally v - shaped notch 155 , called the outflow notch 155 , is created and defined by an outflow flat 162 and an outflow side wall 158 of the diamond surface 154 . as previously discussed herein , washing of the various surfaces , crevices and the like by blood fluid passing through the heart valve prosthesis 110 is believed to be particularly important to reduce stagnation and potentially thrombogenic activity . the present bileaflet heart valve 110 is designed with this in mind . all of the surfaces of the present valve 110 are actively washed at one time or another in the pumping cycle of the heart in which the valve 110 is implanted . when the valve 110 is in the fully opened position all of the surfaces of the side wall 126 are actively washed by blood flowing over the surfaces , as are the recesses 132 . the leaflets 114 are also actively washed as the blood flows in the antegrade direction through the bore 116 . the diamond - shaped cylindrical surface 154 also has a cylindrical radius generally consistent with the cylindrical radius of the bottom surface 140 of the recess 132 . as shown particularly in fig2 , when the leaflets 114 are in a fully closed position , some regurgitation of blood through the bileaflet valve 110 occurs in the retrograde direction . the regurgitation is desirable to a certain degree , so long as the energy efficiency of the pumping activity of the heart is not compromised . the regurgitation occurs in a number of areas . referring now also to fig2 , and the other illustrations of the preferred bileaflet heart valve 110 , retrograde blood flow may pass between the mating surfaces 148 of the respective leaflets 114 as demonstrated by arrows 194 , 195 and 196 in fig2 . the bottom of the leaflets 114 also channel retrograde blood flow into the recesses 132 by directing the blood against the seats 136 created by the separation between the cylindrical bottom surface 140 and the upper edge 134 of the recesses 132 . an outflow side wall 158 of the diamond surface 154 may also channel retrograde blood flow to the recesses 132 and particularly to the seat 136 . this flow will then regurgitate between the leaflet 114 and the side wall 126 after it flows over the seat 136 and come out proximate the regurgitation representation arrows 191 , 192 and 193 . it will be appreciated that flow through areas where the top planar surface 142 meets the seat 136 will be minimized and that this flow can be further minimized by widening the seat 136 further into the transverse side 131 . additional retrograde blood flow will wash other portions of the valve 110 , especially portions of the inner wall 126 , including the lateral depressions 135 and the flat portions of the lateral surfaces 133 , and channel upwards proximate arrow 192 in fig2 . it will be appreciated that there will almost always be at least some separation between the peripheral edge 150 of the leaflet 114 and the side wall 126 . this enables retrograde blood flow to regurgitate between the peripheral edge 150 and the side wall 126 proximate the entire peripheral edge 150 . even where the top planar surface 142 of the respective leaflets 114 are pressed against the respective seats 136 , there is at least some space between the opposing surfaces for a very limited amount of “ regurgitating ” retrograde blood flow . the regurgitation is particularly significant proximate the transverse sides 131 . this is particularly true because of the side wall surface 126 proximate the center of the peripheral edge 150 is flush , thereby providing no obstruction to the retrograde flow of blood . it will be appreciated that the seat 136 is fully diminished to nothing in this area in preferred embodiments . a further discussion of the seats 136 follows a further description of the leaflets 114 immediately below . referring now particularly to fig1 - 21 , a certain amount of “ play ” exists between the respective surfaces in the area of the diamond surface 154 and the recess 132 when the leaflets 114 are in the open position . this “ play ” permits a significant amount of translational movement . because of the increased potential for translational movement between these surfaces when in the open position , the leaflets 114 have greater freedom for translational motion than is either exhibited or generally possible in any of the prior art valves which have “ matched ” or “ parallel ” surfaces in both the open and closed positions . as shown diagrammatically in fig1 , when the leaflets 114 are in the fully closed position , the top planar surface 142 is pressed against the seat 136 proximate the upper edge 134 of the recess 132 . although considerable separation appears to exist between these surfaces in fig1 , this separation is exaggerated for clarity . during use of the valve 110 , the top planar surface 142 abuts against the seat 136 . in actual fact , the spacial relationship between the top planar surface 142 and the seat 136 , when the leaflets 114 are in the closed position , is that shown in fig2 , where the seat 136 cannot be separately called out because it is not visible in the view . an axis 165 , parallel with respective cylindrical surfaces on diamond - shaped cylindrical surfaces 154 of the respective leaflets 114 , and perpendicular the top surface 142 will lie at an angle “ k ” to an axis 167 , parallel with the respective cylindrical bottom surface 140 of respective recess 132 , and perpendicular with the upper edge 134 of the recess 132 , when the leaflets 114 are in the fully opened position . when the leaflets 114 are in the fully closed position these respective axes 165 and 167 will be either superimposed upon one another , or in parallel with one another and the angle “ k ” will generally be about zero . in this position , therefore , the cylindrical surfaces 140 will be “ matched ” or “ parallel ” with the diamond - shaped surfaces 154 of the respective lateral sides 151 of the respective leaflets 114 . the angle “ k ”, shown diagrammatically in fig1 , is equal to the travel angle “ k ′”, when the leaflets 114 are in the fully open position . it will be appreciated that significant translational movement is permitted when the leaflets 114 are in the open position . this can be seen in fig1 where the first axis 165 of the leaflet 114 lies at an angle “ k ” with respect to the second axis 167 of the cylindrical recess bottom surface 140 . this translational movement of the leaflet 114 , when in the fully open position , is believed to allow the leaflet 114 to move from its fully open position to its fully closed position much faster than prior art devices . this is because the initial movement , when a retrograde flow of fluid begins , is an upward translational movement of the diamond - shaped surface 154 within the recess 132 , until the top side fulcrum edge 166 engages the upper edge sidewall or seat 136 within the recess 132 . when the top side fulcrum edge 166 engages the seat 136 within the recess 132 , the leaflet 114 has already overcome any inertia it may have had when “ resting ” in the fully opened position . the translational movement will subsequently give way to pivotal movement of the leaflet toward the fully closed position . this pivotal movement will occur rapidly since the initial translational movement will provide some momentum which will be translated into pivotal or annular movement toward closure of the leaflets 114 . when the leaflet 114 is in the fully closed position , the initial movement of the leaflet is more likely to be followed immediately by a pivotal movement , because the cylindrical diamond - shaped surface 154 and the cylindrical recess bottom surface 140 are more closely mated as shown in fig2 and the separation allowing translational movement from end to end is more limited . the leaflet 114 is likely to slip quickly from the upper side edge 134 toward the lower side sidewall 138 of the leaflet 114 . the leaflet will only begin to pivot after the bottom side fulcrum edge 164 is engaged with the lower side sidewall 138 . it will be appreciated , however , that the mechanism employed by the respective leaflets for pivoting is still a matter of inquiry and is not fully understood at this time . it is believed , however , this dynamic pivot mechanism allows for faster opening and closing of the respective valves 110 . when the valve is in the open position , and the flow direction changes from antegrade to retrograde , it is believed that the leaflet 114 begins its linear motion immediately with the change in the flow direction and the linear momentum is transferred into angular momentum as soon as the top side fulcrum edge or pivot 166 contacts the seat 136 proximate the upper edge 134 of the recess 132 . this is believed to result in quicker closing than is exhibited by prior art devices . it is believed that the preferred bileaflet heart valve prosthesis 110 of the present invention provides for a lowered thrombus potential due to the consideration given to access for washing in both the antegrade and retrograde directions . furthermore , the dynamic pivot mechanism of the preferred leaflets 114 in cooperation with the preferred recesses 132 are believed to provide for faster opening and closing of the valve and less friction in the pivot area due to the use of a “ rolling ” pivot mechanism wherein the pivot activity changes focus from the top side fulcrum edge 166 to the bottom side fulcrum edge 164 . the preferred valve 110 also provides for a minimized travel angle “ k ′” between the fully opened position and the fully closed position . it is believed that the travel angle provided in the preferred valve 110 may represent at least about 15 - 10 ° reduction in the travel angle as compared to many of the prior art devices . this reduction in the travel angle is believed to minimize angular velocity , wear , cavitation potential , and regurgitation volume , while increasing overall efficiency . the upper edges 134 for the preferred leaflets 114 are believed to slow the leaflet 114 just before closure due to the presence of significant amounts of fluids which may be “ squeezed ” or compressed against the sidewall 126 of the annular base 112 . because the seats slow the leaflet 114 just before closure , they are believed to have a minimizing effect on the cavitation potential . it is also believed that the use of discontinuous seats , or seats which diminish prior to continuing into a seat extending from an opposite recess allows for a slight increase in regurgitation potential proximate the center portion of the leaflet where cavitation potential is generally highest due to the likelihood that this area is likely to be subjected to a greater angular velocity as it comes toward closure against the sidewall 126 . the seats 134 also decrease leakage or regurgitation proximate the lateral sides 129 of the annular base 112 when the leaflets 114 are in the closed position . the seats 134 are also believed to provide for increased antegrade flow to wash the flow channels or recesses 132 as the leaflets 114 close . as the leaflets 114 close the fluid in the recesses 132 begins to be “ squeezed ” or compressed within an upper portion of the recess distal to the transverse sides 131 of the annular base 112 . the width of the seats 134 decreases as they extend from the recess 132 to the transverse side 131 . since there is no seat 134 in the center most region of the transverse side 131 in the preferred bileaflet heart valve 110 , the fluid “ squeezed ” or compressed against the seats 134 is generally believed to be released through the bore 116 after it washes at least a portion of the seat 134 . while the leaflets 114 are in the closed position , the seats 134 serve to reduce retrograde leakage or regurgitation and at least a portion of the retrograde flow is channeled around the diamond surface 154 , so as to thoroughly wash these areas when the leaflets 114 are in a closed position . the bottom surface of the recess 132 is in the form of a curvilinear cylindrical surface and is considered to have a generally cylindrical shape . as used herein , cylindrical surface or cylindrical shape means a surface formed by linear translation of a curve , or a surface which has a radius similar to a portion of a surface of a cylinder . the diamond surface 154 at the lateral sides 151 of the leaflets 114 have a cylindrical shape which is “ consistent ” with or “ mates ” with the cylindrical recess bottom surfaces 140 of the recesses 132 . however , as shown in fig2 , the diamond surface 154 is consistent with and mates with the bottom surface 140 of the recess 132 only when the leaflet 114 is in the closed position . however , when the leaflet is in the open position , as shown in fig2 , and as previously discussed , significant room for translational movement is provided . furthermore , it will be appreciated that the bottom surface of the recess 140 and the matched cylindrical diamond surface 154 of the leaflet 114 will not be in alignment when the leaflet is in any position other than a fully closed position , thus allowing for significant clearance between the extreme edges of the diamond surfaces 154 and the extreme edges of the recesses 132 . because of the increased potential for translational movement when the leaflets 114 are in positions other than the fully closed position , the leaflets 114 will exhibit greater translational freedom for motion than is possible with prior art valves having parallel or matched surfaces in all positions as described and defined in descriptions of the prior art devices . as shown particularly in fig1 , the flat planar surface 146 of the central bevel 145 and the peripheral bevel 144 of the bottom surface of the leaflet each lie generally in a plane respectively designated by tangent lines 172 and 174 . as measured by the angle “ a ” between tangent lines 172 and 174 , the peripheral bevel 144 and the flat planar surface 146 of the central bevel 145 lie generally in planes which lie at an angle to one another . in preferred embodiments this angle will be less than 180 °, or preferably at an angle of about 161 ° to about 178 °, more preferably about 166 ° to about 173 °. in preferred embodiments , the angle “ a ” will be about 167 ° to about 172 °. in the most preferred embodiment under consideration , the angle “ a ” is about 169 °. this bevel in the bottom surfaces of the leaflet 114 , allows the angle of incidence for a flow of blood in the retrograde direction parallel with the longitudinal axis 128 to be a greater angle of incidence in respect to the peripheral bevel 144 than with the flat planar surface 146 of the central bevel 145 . this is believed to be advantageous for at least two reasons . first , since there is a greater angle of incidence , the force of the blood flowing in the retrograde direction will have greater impact upon the leaflet 114 and cause it to pivot toward the fully closed position more rapidly than might otherwise be expected . furthermore , the difference between the respective bevels , and the angle of the tangent line 176 to the top planar surface 142 allow the peripheral edge 150 to have a shorter radial closing distance to travel before the leaflet 114 is in the fully closed position than might be expected for a leaflet having parallel surfaces . in preferred embodiments , the angle of the plane in which the flat planar surface 146 of the central bevel 145 rests , to a horizontal plane 170 , which angle is consistent with the angle between tangent line 172 and the plane 170 , will be an angle “ a ′”. in preferred embodiments , “ a ′” may range from about 84 ° to about 97 °, preferably about 86 ° to about 95 °, more preferably about 88 ° to about 94 °, more preferably about 90 ° to about 92 °, more preferably more than 90 °, and in the most preferred embodiments , “ a ′” will be either 91 °, or 91 ° or more . similarly , the angle between the plane in which the peripheral bevel 144 rests , and the horizontal plane 170 may be measured by taking the angle “ b ′” between the tangent line 174 and the horizontal plane 170 . in preferred embodiments , the angle “ b ′” will be less than 87 °, preferably less than 86 °. in preferred embodiments , “ b ′” will range from about 78 ° to about 84 °, preferably about 80 ° to about 82 °, and most preferably , it will be about 81 °. similarly , the angle of the plane in which the top planar surface 142 of the top side of the leaflet 114 rests , will lie at an angle “ c ′” to the horizontal plane 170 as measured between the tangent line 176 and the horizontal plane 170 when the leaflet is in the fully open position . in preferred embodiments , “ c ′” is greater than about 78 ° and less than 90 °, and preferably in a range of from about 82 ° to about 89 °, preferably about 84 ° to about 88 °. in the most preferred embodiment , “ c ′” is about 86 °. as shown particularly in phantom in fig1 , when the leaflet 114 begins to pivot from the fully open position to the fully closed position in response to force exerted upon the peripheral bevel 144 , the force is believed to result in an initial translational movement of the leaflet to lift leaflet 114 within the recess 132 . when the leaflet 114 has reached the fully closed position shown diagrammatically in fig1 , an area on the top planar surface 142 proximate the peripheral edge 150 generally proximate the respective lateral sides 151 will abut against the seat 136 on either lateral side 129 and extending at least partially into the adjacent transverse side 131 . when the leaflet 114 is in the fully closed position , the respective mating edges 148 will generally rest against one another while generally allowing at least some retrograde regurgitation of blood between the respective mating surfaces 148 . it will be appreciated that the preferred embodiment of the bileaflet heart valve prosthesis 110 of the present invention will not have any sharp edges and that all edges will in fact be polished , smoothed or feathered so as to minimize shearing of blood as it passes over any of these edges . these smooth “ transitions ” between surfaces of all kinds will be obtained by shaving and polishing all edges so that the edges are rounded and have a smooth transition from one plane to another . any radial surfaces of course will be polished as well . as shown in fig2 , the amount of regurgitation of blood in the retrograde direction is believed to be significant enough to provide appropriate cleansing of the valve 110 . heart valves are generally designed with at least some regurgitation in mind so long as the regurgitation does not reduce the efficiency of the heart . it is believed that the regurgitation is important to permit the washing of the various surfaces of the present prosthetic device . fig2 generally provides a representation of the quantity ( q ) of blood flowing through a bileaflet heart valve during a contraction cycle when the valve is in the aortic position . during systole , the quantity of blood passing through the valve in the antegrade direction (+) is fairly significant . as the force from the contraction diminishes from its highest point , indicated at the apex of the curve ( qsys ), until the antegrade flow ends and blood begins to flow in the retrograde direction (−), the leaflets 114 remain in an open position . the retrograde flow then begins to push the leaflets 114 toward the closed position at the lowest point of the curve below the “ y ” axis ( qcl ). as the leaflets 114 close , most of the retrograde flow is obstructed , but not all of it . the remaining retrograde flow is due to leakage around the leaflets 114 . the retrograde leakage ( ql ) has been discussed herein and is believed to have a positive effect in respect to washing the various surfaces of the prosthetic heart valve , in that this “ regurgitation ” will “ wash ” the surfaces to reduce stagnation of blood as a measure against potential thrombus . as shown particularly in fig6 and 7 and demonstrated diagrammatically in fig2 , the upper edge 134 blends or “ feathers ” into the inner wall 126 of the annular base 112 , as does the seat 136 , in preferred embodiments . it is believed that this has a very positive effect upon preservation of the integrity of the top planar surface 142 of the respective leaflets 114 by reducing cavitation potential . this is particularly true in an area approximately 15 ° to either side of a center line 184 bisecting a leaflet 114 , and in the areas most proximate to the peripheral edge 150 . the potential for negative effects of cavitation upon the top planar surface 142 is also reduced by the shortened travel angle “ k ′” between the location of the top planar surface 142 when the leaflet is in the fully open position , and the top planar surface 142 when the leaflet is in the fully closed position as represented by tangent line 179 of fig1 . because the preferred leaflet 114 of the present invention has a “ double - beveled ” bottom surface , the position of the top planar surface 142 in relation to the side wall 126 can be minimized to reduce the radial distance “ k ′” traveled by the top planar surface 142 in moving to the closed position . in this way , the angular speed of the movement of the most distal portion of the top planar surface 142 proximate the peripheral edge 150 , where the cavitation potential is generally believed to be the greatest , is diminished gradually when the leaflet 114 approaches the closed position . cavitation potential is also minimized because the distance is minimized by the beveled design of the leaflets 114 . in this regard , it will be appreciated that the leaflet will continue to gain speed as it pivots through a greater radial distance . therefore , by minimizing the radial distance between the open position and the closed position , the radial speed of the leaflet 114 can be minimized . in preferred embodiments , the travel angle “ k ′” will be from about 37 ° to about 58 °, preferably about 39 ° to about 56 °, even more preferably about 40 ° to about 55 °, and most preferably about 45 ° to about 50 °. cavitation potential is also reduced because the seats 136 , extending from the respective recesses 132 on the respective lateral sides of the leaflet 114 , help to slow the closure or “ cushion ” the closure of the leaflet against the side wall 126 because the blood between the peripheral edge 150 and the proximate portions of the top planar surface 142 must be “ squeezed ” out of the intervening space adjacent the respective seat 136 as the leaflet 114 is pivoting toward the fully closed position . furthermore , a gap 171 ( shown in fig8 ) between the seats 136 of the opposing lateral sides extending into the transverse side permits a continuing flow of blood in the retrograde direction which also helps to prevent the formation of a vacuum on the top planar surface 142 proximate the peripheral edge 150 which is generally the genesis of cavitation damage on the planar surfaces of a leaflet 114 . the “ cushioning ” effect of the partial or “ discontinuous ” seats 136 also helps to prevent stress to other portions of the leaflet 114 as they collide with the side wall 126 or the seat 136 . in fig2 , a center line 184 extending from a center point 182 is shown superimposed upon a bottom surface of a leaflet 114 . in preferred embodiments , the respective seats 136 extending from respective recesses 132 will extend only as far as the radius lines 185 and 186 which are radially equidistance from the center line 184 . for this reason , the radial angle “ i ′” will equal the radial angle “ h ′” between the radius lines 186 , 185 and the center line 184 , respectively , and the radial angle “ j ′” will equal twice either of the equal angles “ i ′” and “ h ′”. in preferred embodiments , the radial angle of “ j ′” will range from about 5 ° to about 55 °, preferably about 10 ° to about 50 °, more preferably about 15 ° to about 45 °, even more preferably about 20 ° to about 40 °, even more preferably about 25 ° to about 35 °, and even more preferably about 30 °. the reason for limiting the extension of the seats 136 entirely through the inner wall 126 proximate the transverse surface 131 is in part because of a desire to minimize the cavitation potential which is generally greatest within 15 ° on either side of a center line 184 bisecting the top planar surface 142 of a pivotal leaflet 114 of a bileaflet heart valve . it will be understood that the area having the greatest cavitation potential is likely to be at the most distal portion of the top planar surface 142 from the center point 182 , because it is this portion of the leaflet 114 which gains the most angular speed when the leaflet is pivoting toward closure and is most capable of generating the force required to create cavitation bubbles on the top planar surface 142 . therefore , eliminating the seat 136 in this particular area , is expected to minimize cavitation potential by permitting more regurgitation through the gap 171 . while the preferred embodiments of the above bileaflet heart valve 10 , 110 have been described in detail with reference to the attached drawings , it will be understood that various changes and adaptations may be made in the bileaflet heart valve 10 , 110 without departing from the spirit and scope of the appended claims . it is to be understood that even though numerous characteristics and advantages of various embodiments of the present invention have been set forth in the foregoing description , together with details of the structure and function of various embodiments of the invention , this disclosure is illustrative only and changes may be made in detail , especially in matters of shape , size and arrangement of parts , within the principles of the present invention , to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed .
a bileaflet heart valve comprising an annular base and pivoting leaflets . each leaflet is “ free - floating ” within recesses without fixed rotational axis in order to increase translational movement and redistribute stresses . each recess fluidly communicates with a groove extending at least partially around the inner surface of the annular base and fluid flow is directed through the recesses at different angles during antegrade circulation , retrograde circulation , and valve closure . a recess entrance angle to each of the recesses preferably being less than about 35 ° and the pivoting mechanism within the recess including first and second fulcrum edges of each leaflet shiftably engaged with side surfaces of the respective recesses . the leaflets have a beveled bottom side having two separate planar surfaces which lie at an angle to one another . in preferred embodiments , an upper planar surface of the bottom surface of each leaflet lies at an angle of greater than ninety degrees with respect to a horizontal passing through a section of the annular base when the leaflet is in a fully open position .