Abstract
In sheep, stented pulmonary semilunar valves have been allografted as tricuspid valve substitutes and their biological behaviour has been followed postoperatively. Whereas there was initial pleasing function with normal cusp competence, by day 102 the cusps had retracted to partial incompetence. This process of valve decline was accentuated by day 150, and by day 241 was complete. Histological studies at day 150 showed cusp foreshortening, with scant nuclei and collagen looser than normal. These findings suggested that the mechanism causing the valve decline was a host to foreign body reaction rather than the usual histological pattern of graft rejection.