"Medical" complications occur more frequently, and are more hazardous, in patients who have had a valve replacement. In 59% of the patients a prosthetic valve was inserted, but 73% of the deaths and 70% of the complications occurred in this group. These patients were older, and in general their cardiac disease was more advanced than the patients undergoing other operative procedures. The longer durations of anesthesia, operation, and cardio-pulmonary bypass in patients requiring valve replacement also contributed to the increased incidence of postoperative complications in these patients. Embolization, hemolytic anemia, and hemorrhage resulting from anticoagulants in patients with prosthetic valves, the development of serum hepatitis, the persistence of myocardial failure, pulmonary hypertension, and tricuspid regurgitation and problems that are most frequently dealt with in the late postoperative period.