We reviewed data of 64 patients who underwent reoperation because of prosthetic valve malfunction from January 1991 to December 1995. The indications for reoperation were prosthetic valve failure(primary tissue failure: 53 patients, 82.8%), prosthetic valve thrombosis(6 patients, 9.4%), paravalvular leak(3 patients, 4.7%), prosthetic valve endocarditis(2 patients, 3.6%). Prosthetic valve failure developed most frequently in mitral portion(40 patients, 75%), prosthetic valve thrombosis also in mitral portion(4 patients, 67%), paravalvular leak significantly in aortic portio (3 patients, 100%). Explant period was longest in prosthetic valve failure(mean 107.4 $pm$ 24.6 months), shortest in prosthetic valve endocarditis with prosthetic valve thrombosis(1 patient, 1 month). Mean explant period, defined as from first valve replacement operation to redo-valve replacement operatopn, was 109.2$pm$ 10.7 months in mitral portion, 97.8$pm$ 10.4 months in aortic portion, 109.5$pm$ 10.4 months in total. Overall hospital mortality was 9.38%. The most common cause of death was the low cardiac output(4 patients), other causes were bleeding(1 patient), CNS injury(1 patient). Preoperative NYHA class IV(P=0.011), emergency operation(P=0.011), prosthetic valve endocarditis(P=0.001) were the independent risk factors, but age, sex, explant period, ACC time, double valve replacement, valve position, second reoperation did not appear to be significant risk factors. Mean follow up period was 28.8 $pm$ 17.8 months. Actuarial survival at 3 year was 92.0$pm$6.2%, 2 year event-free survival w s 84.3$pm$6.1%. We propose that patients undergoing reoperation because of prosthetic valve failure are carfully controlled and selected in regarding to above mentioned risk factors NYHA class IV, emergency operation, prosthetic valve endocarditis in preoperative state. About other risk factors possible, there is necessary of following study.