CLINICAL introduction of the pump oxygenator approximately ten years ago opened an entirely new field in the surgical therapy of heart disease. Direct operative exposure of numerous congenital intracardiac lesions then paved the way for development of surgical techniques now employed daily for successful correction of these anomalies. For many years, however, surgical therapy of acquired valvular heart disease remained limited by the state of the diseased valve. Stenotic valves, particularly the aortic, frequently contained extensive calcific deposits in addition to fibrous tissue thickening which precluded adequate debridement and mobilization of the leaflets, even using currently available sophisticated instrumentation. Although transventricular mitral commissurotomy proved to be an effective procedure in most cases of mitral stenosis,1 such a procedure was inadequate in a significant number of patients, and aortic commissurotomy for acquired lesions far too often was followed shortly by restenosis or development of valve incompetence. In the majority of