Although disc valves have been used extensively for mitral valve replacement, few long-term hemodynamic studies are available. Twenty-five patients received a Kay-Shiley valve, and hemodynamic studies were obtained in 17 patients at an average interval of 15 months after operation. Left ventricular cineangiograms revealed mitral insufficiency in 8 of 15 patients. In three patients a poorly contracting myocardium was associated with elevated left ventricular end-diastolic pressures, suggesting the possibility of acquired endocardial fibroelastosis. The embolic rate was 38%. Two valves became severely stenosed, and two had severe paravalvular leaks which required replacement. Although most patients were improved symptomatically and hemodynamic studies revealed improvement, all had abnormal valve function, particularly during exercise.