Reflections on the development of valvular prostheses.

Surgical attempts to open obstructed heart valves in the 1940s led to the eventual development of valvular prostheses, accompanied by the parallel development of methods of sustaining extracorporeal circulation; biocompatible materials; and engineering designs. Early problems encountered included the incidence of thrombotic phenomena, audibility of valvular noise, impaired flow dynamics, and hemo-incapability. These problems have been solved with increasing success with the creation of new plastics, the ball valve design, and improved manufacturing processes.