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SEVERAL REPORTS have appeared in the literature indicating that ball valve aortic prostheses usually produce some residual obstruction.1-4 It has often been assumed that the residual pressure differences across these valves is due to the small orifice area of the prosthetic valve ring compared to that of a normal aortic valve. In contrast to this concept, our results indicate that even when the orifice area of a ball valve approaches normal values, obstruction may exist and that for all valve sizes the resistance to flow is greater than might be expected from a knowledge of its orifice area. We would also like to emphasize the not infrequent occurrence of an obscure form of myocardial insufficiency which is in many cases responsible for the abnormal exercise response noted in these patients.

The Hemodynamics of the University of Cape Town Aortic Prosthetic Valve