Equal to the performance of a good operation is the selection of the correct operation. The preferred operation is the one that enables the patient to remain alive and well for the longest time. Therefore, the selection of the optimal procedure requires information concerning the late results of operations that are available. Such information is most meaningful when it includes percentages of patients alive and well at various time intervals since operation, for it can then be utilized to evaluate the effect of preoperative characteristics or operative maneuvers on the late results of the operation. Only time-oriented data involving follow-up periods of variable lengths allow accurate comparisons. The purpose of this report is to present the results of aortic valve replacement using the ball-valve (Starr-Edwards) prosthesis and to define factors which significantly influence these results in the early as well as the late postoperative period. Materials and Methods Up to