The increasing number of replacement of the substitute cardiac valves were seen in these 2 years. Out of a total 1,408 patients with cardiac valve replacement, 54 required replacement of the substitute valves. Fifty-nine substitute valves replaced were 43 in mitral, 14 in aortic and 2 in tricuspid positions; and they were 36 Ionescu-Shiley, 15 Hancock and 3 Angell-Shiley bioprosthetic valves and 3 St. Jude Medical and 2 Bjork-Shiley prosthetic valves. Primary tissue failure was the most frequent reason of replacement[38 patients] followed by paravalvular leak[9 patients], prosthetic valve endocarditis[6 patients] and valve thrombosis[1 patient] in order. The most pronounced pathology of the failed xenograft valves seen in the primary tissue failure group was calcification and fixation of the cusps with or without tear and defect of the cuspal tissue. The operative mortality rate was 7.4%. Fifty early survivors were followed up for a total of 82.6 patient-years and there was no late death. Actuarial survival rate was 92.3*3.8% at 6 years after surgery. Although the definite tendency toward early and accelerated degeneration of the xenograft valves has been seen in patients younger than 20 to 25 years of age, no strict age limit from where the tissue failure slows down could be determined. The requirement of the ideal substitute valves would be the durability of the recently developed mechanical prostheses armed with the low thrombogenicity of the bioprostheses. At the present time, the need of compromise in selection between less thrombogenic bioprosthetic and more durable mechanical valves should be stressed. The difficulty in choice is yet important in patients of middle age and children where the use of homograft valves may be one of the solution despite of certain limitations from sociomedical reasons.