Revascularization of the myocardium was performed in 25 patients two to eight hours after acute myocardial infarction (MI). The intra-aortic balloon pump was used in 11 patients. Thirteen patients received revascularization within four hours of onset of MI; all survived the operation. Seven patients were studied postoperatively; ten of 12 grafts (83%) were patent. There was a considerable decrease in left ventricular (LV) dyskinesis and an improvement in LV function. Among 12 patients in whom revascularization was performed for more than four hours' duration after the onset of MI, ten survived. Six were studied postoperatively; six of nine grafts (66%) were patent. There was an increase in LV dyskinesis, with deterioration in LV function. In three patients, ECG evidence of Q wave persisted in spite of absence of dyskinesis postoperatively. The interval during which revascularization of acute infarction produces acceptable results in less than four hours.