From 1975 to 1980, 112 patients with an ejection fraction below 45% underwent coronary artery bypass grafting (CABG) in the Cardiovascular Surgery Unit, University Hospital Zürich. The mean age was 35 years and the mean ejection fraction 32% (21-44%). The vast majority of patients had severe symptoms (angina pectoris or congestive heart failure). Elective surgery was performed in 62 patients (55%) and emergent or urgent in 50 (45%). All were operated on in mild hypothermia (26-30 degrees C). An average of 2.9 bypasses per patient were performed; in 57, internal mammary artery bypass was carried out for revascularization of the left anterior descending branch. - Early postoperative mortality (within 30 days of operation) was 3.6%; all deaths were of cardiac origin. Perioperative myocardial infarction occurred in 7.5% of all patients. Cumulative survival was 83% at 5 years and 68% at 9 years. Mean mortality rate/year was 3.8% with a maximum of 6.5% in the first year after operation. The incidence of angina pectoris and congestive heart failure was significantly lower after revascularization. Cumulative survival was significantly enhanced in patients with complete revascularization (91% at 5 years vs 71% for incomplete revascularization). Early postoperative mortality was especially high in urgent and emergent cases, and was higher after revascularization with internal mammary artery bypass than with venous graft. Postoperative ejection fraction was assessed in 20 patients (12 with 2- or 3-vessel disease and 8 with left main coronary artery stenosis). Ejection fraction was significantly increased only in the patient group with left main coronary artery stenosis.(ABSTRACT TRUNCATED AT 250 WORDS)