All cases of coronary bypass procedures without concomitant heart valve replacement occurring in a defined geographical area over a 8-year period (1980-1987) were reviewed and the 30-day mortality and complication rates associated with them were analyzed. The study comprised 3,484 patients with the diagnoses: stable (2477) or unstable (724) angina pectoris, angina pectoris combined with left ventricular aneurysm (165) or with an other complicating factor (96), postinfarction septal defect (13) and postinfarction mitral valve insufficiency (9). The total operative mortality during the study period was 3.1%. Persistent new Q waves in the electrocardiogram developed in 2.4% and increased enzyme release indicating myocardial injury (S-ASAT greater than 2.0 microkat/L and S-CKMB isoenzyme greater than 1.5 microkat/L) occurred in 15%. There were 478 complications in 378 patients (11%). Indication for surgery, year of surgery, NYHA class, congestive heart failure, age, sex, aortic cross-clamp time, and cardiopulmonary bypass time were significantly related to operative mortality (p less than 0.05). The same variables except sex were related to complications. Myocardial infarction (new persistent Q wave) was predictable by NYHA class, aortic cross-clamp time, and cardiopulmonary bypass time. The same variables and also year of surgery, regrafting procedure, congestive heart failure, and thromboendarterectomy were predictors of myocardial injury (enzyme release).