The records of 288 patients undergoing isolated surgical myocardial revascularization between June 1989 and September 1992 were reviewed to determine the relative risk associated with surgery after an acute myocardial infarction (MI). A total of 73 patients (25 percent) were operated on within 30 days of an acute infarction while 215 patients (75 percent) had no history of recent infarction. Patients with an acute infarction were more likely to have regional wall motion abnormalities on ventriculography (mean wall score 6.7 vs 4.9, p = 0.001), require preoperative balloon pumping (15.1 percent vs 5.6 percent, p = 0.01), and have recent symptoms of congestive heart failure (23 percent vs 12 percent, p = 0.02). Patients with an acute MI also had higher NYHA functional classification and greater urgency of surgery. Despite these differences, overall mortality was lower in the acute MI group than in the control population (1.4 percent vs 2.3 percent, p = 0.623). Weaning from bypass was not appreciably more difficult in patients with an acute MI, nor were there differences in the mean number of hours of balloon pump or inotrope support.