Among 3,707 patients who underwent aortocoronary bypass, 302 had preinfarction angina. Coronary angiography revealed single-vessel disease in 43 patients, double-vessel disease in 81, and triple in 178 patients. Plane ventriculography showed contractility to be normal in 178 patients, fair in 88, and poor in 36 patients. Left ventricular end-diastolic pressure was normal in 203 patients, 13 to 23 mm Hg in 73, and larger than or equal to 24 mm Hg in 26 patients. Using cardiopulmonary bypass and moderate hypothermia, single coronary bypass was performed in 45 patients, double bypass in 120 patients, triple in 118 patients, quadruple in 15, and quintuple in 4 patients. Right coronary artery endarterectomy was necessary in 22 patients. The early mortality was 6.6% (20 patients) and was strongly related to poor contractility and congestive heart failure. One- to four-year follow-up data were obtained in 126 patients. Late myocardial infarction occurred in 11 patients and caused 4 late deaths; 3 unrelated deaths occurred. Ten patients experienced no benefit from their operations, 56 are completely asymptomatic, and 53 are significantly improved. Our results show that surgical intervention can improve the poor prognosis of preinfarction angina and appears to be superior to medical treatment.