To determine the potential benefit of myocardial revascularizations in acute myocardial infarction we analyzed a consecutive series of 641/3397 patients with stable or unstable angina in Canadian Heart Association Class IV divided into five groups: A) unstable angina (ECG S-T modifications), B) evolving infarction (new Q-wave, CK more than 3 times normal), C) mechanical complications (ventricular septal defect (VSD), wall rupture, acute mitral regurgitation), D) coronary artery occlusion (crashed percutaneous transluminal coronary angioplasty (PTCA)), and E) stable angina class IV (control group). The mean follow-up was 72 +/- 33 months (range 24-144 months). Of the 641 patients 362 were unstable (A), 22 had evolving infarction (B), 20 suffered from mechanical complications (C), 48 had acute coronary artery occlusion (D), and 189 were in the control group (E). There was no difference for left ventricular (LV) ejection fraction before surgery (P < 0.05 = * as compared to control (E)), however cardiogenic shock was present before surgery in 13/362 (4%) for unstable angina, 5/22 (23%) for evolving infarction, 6/20 (30%) for mechanical complications, 4/48 (8%) for acute occlusion, and none of the controls. The number of bypasses was 3.8 +/- 1.3* for unstable angina, 3.6 +/- 1.3 for evolving infarction, 2.3 +/- 1.2* for mechanical complications, 2.0 +/- 1.2* for acute occlusion, and 3.4 +/- 1.5 for control. Intra-aortic balloon pumping was necessary in 26/362 (7%) for unstable angina, 5/22 (23%*) for evolving infarction, 7/20 (35%*) for mechanical complications, 7/48 (15%*) for acute occlusions, and 5/189 (3%) of the controls.(ABSTRACT TRUNCATED AT 250 WORDS)