Prosthetic valves in children and adolescents. The purpose of this paper is to present the short- and long-term results of prosthetic valve replacement in children. During a 7-year period that ended in April 1985, 186 children, ages 1 to 20 years, underwent valve replacement; there were 55 (30%) aortic valve replacements, 95 (51%) mitral valve replacements, and 36 (19%) multiple valve replacements. Ninety-four percent of the lesions were rheumatic in origin, 4% were congenital, and 2% were infectious. Of 223 valves replaced, 175 (78%) were mechanical valves and 48 (22%) were heterografts; the latter were in the mitral position in all but three patients. Surgical mortality rates were 3.6%, 4.2%, and 19.4% respectively for aortic valve, mitral valve, and multiple valve replacements. Five-year actuarial survival was 91% for aortic valve replacement, 82% for mitral valve replacement and 60% for multiple valve replacement. Major events included reoperation in 34 (with three deaths), progressive myocardial failure that led to death in 10, sudden unexpected death in two, thromboembolic complications in 19 (death in five), subacute bacterial endocarditis in five (two deaths), and bleeding that required transfusion in two patients. Five-year complication-free actuarial survival rates were 83% for aortic valve replacement, 63% for mitral valve replacement, and 57% for multiple valve replacement. The respective five-year complication-free survival rates were 83%, 48%, and 43%. Significant morbidity and mortality rates are associated with valve replacement. Therefore every effort should be made to preserve the native valve by plastic reparative procedures. When prosthetic replacement of mitral valve is contemplated, our data would suggest that heterografts should not be inserted in children 15 years of age or younger, although heterografts may be used in children over 15 years of age with the expectation of valve survival comparable to that of mechanical valves. When complications that are associated with anticoagulant therapy were reviewed, platelet inhibiting drugs seem quite satisfactory in patients with aortic valve replacement; patients with mitral valve replacement seem to require warfarin therapy, and warfarin must be used in patients with multiple valve replacement to reduce the risk of thromboembolic complications. 