Clinical experience with the Medtronic-Hall valve prosthesis. Medtronic-Hall valves were implanted during 204 procedures performed between 1982 and 1988. Mean population age was 54.4 years; 96% of patients were in New York Heart Association functional class III or greater. Emergency operations constituted 16% of the procedures. Rheumatic heart disease was the single most common indication for valve replacement. In 18% of patients, operation was performed to replace a previous prosthetic valve. The mean follow-up was 3.2 years. Overall operative mortality was 10.3%, the highest mortality being for double-valve replacements (24%). Valve-related mortality, by position, was 5.3% for aortic valves, 6.0% for mitral valves, and 4.0% for multiple-valve replacements. Actuarial 5-year freedom from events were: survival, 68%; thromboembolism, 90%; prosthetic valve endocarditis, 98%; paravalvular leak, 95%; and reoperation, 92%. Complications with the highest mortality were thromboembolism (36%) and endocarditis (33%). The complication rates in this series are high but the patients were more severely ill than in other reports, and operative survivors experienced a considerable improvement in New York Heart Association functional class. 