In a prospective randomized trial, 468 patients with unstable angina pectoris who were stratified according to clinical presentation (Type I or Type II angina) and left ventricular function (normal or abnormal) were assigned to medical or surgical treatment groups. Left ventricular function was defined as abnormal if the ejection fraction was less than 0.50, or if the end-diastolic pressure was 16 mm Hg or greater. Left ventricular function was abnormal in 134 patients, 66 of whom were assigned to surgical and 68 to medical treatment groups. The cumulative 3-year mortality for surgical patients was 6.1% and for medical patients, 17.6% (p = 0.039). This 3-year figure represents a 65% reduction in mortality with surgery. Survival was significantly better for surgical patients whose ejection fractions ranged from 0.30 to 0.49 (p = 0.05). Survival of patients whose ejection fractions were greater than 0.69 was better with medical treatment (p = 0.049). Thus, surgery appears to be the treatment of choice for patients with unstable angina pectoris and abnormal left ventricular function.