The effect of using the internal mammary artery (IMA) as a conduit for revascularization on the outcome of early (< 30 days) coronary artery bypass graft surgery after acute myocardial infarction was determined. Forty patients were studied: 27 underwent urgent operation for ongoing ischaemia and/or haemodynamic instability early after acute myocardial infarction and 13 had emergency surgery for failed percutaneous transluminal coronary angioplasty associated with clinical and enzymatic evidence of myocardial infarction. Nine patients experienced low cardiac output before operation, in six of whom intra-aortic balloon counterpulsation was used to treat cardiogenic shock. In 26 patients (group 1) the left IMA was utilized with or without additional vein grafts. In the remainder (group 2, n = 14), only vein grafts were used. Group 1 patients were younger than those in group 2 (mean(s.d.) age 55(9) versus 67(8) years, P = 0.0001). Other preoperative and perioperative variables were similar in the two groups. There was one death in hospital (2%, group 2). Eight (31%) group 1 patients sustained postoperative low cardiac output compared with ten (71%) in group 2 (P < 0.04). Preoperative low cardiac output (P < 0.025) and non-use of the IMA (P < 0.05) were identified by univariate and multivariate analysis as the most significant independent predictors of low cardiac output after operation. Although age was excluded as a predictor of low cardiac output, it is concluded that the IMA is an adequate conduit that can safely be used in patients younger than 70 years of age undergoing myocardial revascularization during or early after acute myocardial infarction.