Eighty-three patients underwent coronary artery bypass during acute evolving myocardial infarction 6.8 ± 2.8 hours after the onset of symptoms. Linear discriminant analysis of preoperative variables identified predictors of mortality with an accuracy of 84%. Significant predictors in decreasing order of importance were cardiogenic shock, age over 65 years, left ventricular ejection fraction ≤ 0.30, cardiac index ≤ 2.0 L/min/m2, and absent collateral flow. Time to reperfusion did not influence outcome nor did the infarct-related artery. Hospital mortality was 15.6% (13/83). Among 51 low-risk patients under 65 years of age without cardiogenic shock, there were three deaths (5.9%). Follow-up angiography was performed in 21 patients. The graft patency rate was 94%. Left ventricular ejection fraction improved from 0.39 ± 0.10 to 0.49 ± 0.11 (p < 0.05). Left ventricular end-systolic volume decreased from 53.2 ± 19.3 ml/m2 to 41.4 ± 16.8 ml/m2 (p < 0.05), and end-diastolic volume remained unchanged: 86.2 ± 21.2 ml/m2 before operation and 78.7 ± 24.0 ml/m2 after operation (no significant difference). Regional ejection fraction of the infarct area, determined by the centerline method, increased 0.23 ± 0.15. In contrast, among 215 patients treated by nonsurgical reperfusion (intracoronary thrombolysis or angioplasty, or both), mortality was 13.5%. In this group, reperfusion was successful in 144 patients (67%) and 89 underwent follow-up angiography. Persistent patency of the infarct artery was demonstrated in 73 (82%). Ejection fraction increased from 0.45 ± 0.10 to 0.50 ± 0.15 (p < 0.05). We conclude that preoperative variables enable identification of patients with evolving acute myocardial infarction in whom coronary artery bypass is associated with low operative mortality and improved ventricular performance.