a pump according to the invention is shown in the drawings to comprise an inner flexible , resilient tube 20 having an inlet end 21 and an outlet end 22 . the wall 23 of tube 20 is provided , at a medial site between ends 21 and 22 , with a field 24 of perforations 25 . inlet end 21 is to be connected to a catheter in a patient &# 39 ; s femoral artery or other advantageous source of patient &# 39 ; s blood , and outlet end 22 is to be connected to a cta / cp catheter or other perfusion apparatus . an outer flexible resilient tube 26 , of a length somewhat greater than that of the field of perforations in tube 20 , surrounds the inner tube in the region of the field . at its ends 27 and 28 , tube 26 is secured in fluid tight relation around tube 20 . the dimensions of the tube assembly 30 are such that a space 31 between the tubes has a desired volume of , for example , 2 milliliters . the tube assembly is contained in a chamber 32 made up of two portions 33 and 34 interconnected by a hinge 35 and provided with supporting feet 36 . a cavity is formed jointly in portions 33 and 34 along their abutting surfaces , and has a central portion 40 configured to closely enclose tube 26 , and end portions 41 and 42 configured to closely enclose tube 20 where it extends beyond tube 26 . portion 33 is further provided with a bore 43 opening inwardly to central portion 40 of the cavity , and outwardly to a threaded connection 44 for receiving metal tubing . portion 33 is configured with a horizontal ledge 45 at one end and a vertical wall 46 at the other end . a solenoid 47 is mounted on ledge 45 by a clevis 50 and a vertical pivot 51 . portion 34 is configured with a horizontal ledge 52 at one end and a vertical wall 53 at the other end . a solenoid 54 is mounted on ledge 52 by a clevis 55 and a vertical pin 56 . a first bell crank 60 is pivoted on a vertical pin 61 extending upward from ledge 45 . the long arm 62 of the bell crank is pivotally connected by a vertical pin 63 and a clevis 64 to the movable armature 65 of solenoid 47 , and carries a stop screw 66 and lock nut 67 for limiting the inward stroke of the armature by engagement with portion 33 at an abutment 70 . the short arm 71 of crank 60 carries a roller 72 on a vertical pivot pin 73 . a second bell crank 74 is pivoted on a vertical pin 75 extending upward from ledge 52 . the long arm 76 of the bell crank is pivotally connected by a vertical pin 77 and a clevis 80 to the armature 81 of solenoid 54 , and carries a stop screw 82 and lock nut 83 for limiting the inward stroke of the armature by engagement with portion 34 at an abutment 84 . the short arm 85 of crank 74 carries a roller 86 on a vertical pivot pin 87 . the function of solenoids 47 and 54 is to open and close the ends of tube 20 as desired . in fig1 solenoid 47 is shown with its armature retracted , so that stop screw 66 engages abutment 70 . in this situation , roller 73 compresses tube 21 against wall 53 so as to practically close the tube , leaving only a very small gap . solenoid 54 is shown with its armature extended . in this situation , roller 86 disengages tube 20 to enable it to expand to its full diameter . as shown in fig1 bore 43 is connected at 44 by a tube 90 , a tee 91 , and a pair of tubes 92 and 93 , to a pair of valves 94 and 95 which are connected respectively to a source 96 of gas under pressure and a source of vacuum 97 . helium is the preferred gas , and the usual regulators are to be provided for the negative and positive pressure sources . valves 94 and 95 , as well as solenoids 47 and 54 , are controlled by a supervisory apparatus or sequencing switch 100 in a manner shown schematically in fig3 . the sequence of operation is such as to draw blood into tube 20 at end 21 and through apertures 25 into space 31 , then to impel the blood out of space 31 and out of tube 20 at end 22 . to do this , sequencer 100 first retracts armature 81 and opens valve 95 , admitting negative pressure to bore 43 to expand outer tube 26 fully and maximize space 31 , thus drawing blood in at tube end 21 and through apertures 26 into space 31 . valve 95 is then closed , armature 81 is extended , armature 65 is retracted , and valve 94 is opened , admitting helium gas under pressure to bore 43 to compress outer tube 26 and impel the blood out of space 31 through apertures 25 and tube end 22 . the fact that rollers 72 and 86 do not completely close tube 20 does not materially degrade the efficiency of the pump , but does avoid mechanical damage to the blood by crushing any of its cellular components . while sequencer 100 may operate in an arbitrary time sequence , it is desirable that its operation be synchronized or coordinated with the patient &# 39 ; s own heartbeat , and to that end a signal from a suitable sensor may be supplied to sequencer 100 as suggested at 101 . from the foregoing it will be evident that i have invented a safe , reliable pump for supplying , for use in coronary perfusion for example , blood from a patient &# 39 ; s artery . the pump operates in a manner which results in minimum mechanical damage to the blood . it meets all the requirements for use in an operative environment , and is adapted to have its operation coordinated with the patient &# 39 ; s own heartbeat . numerous characteristics and advantages of the invention have been set forth in the foregoing description , together with details of the structure and function of the invention , and the novel features thereof are pointed out in the appended claims . the disclosure , however , is illustrative only , and changes may be made in detail , especially in matters of shape , size , and arrangement of parts , within the principle of the invention , to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed .