Nine patients chosen at random received substrate enhanced cardioplegia (SECP) for early (less than 4 h) revascularization in acute infarction. A control group of 9 patients with similar clinical characteristics was chosen from the larger group revascularized concurrently with a noncardioplegic technique (NCP). There were no significant differences between the NCP and SECP groups respectively in preoperative clinical parameters such as age (62.8 vs. 62.3 years), sex (7 men, 2 women in both groups), ejection fraction (50% vs. 56%) or number of diseased vessels (2.1 vs 2.3). Intraoperative aortic clamp times were significantly shorter in NCP patients (11 vs. 38 min), and 4 NCP patients had no clamping. The internal mammary artery (IMA) was used in 6 NCP patients and 1 SECP patient (to a nonoccluded branch vessel). Postoperatively, NCP patients had higher peak CPK-MB (284 vs. 190 IU/l), longer use of inotropes (10 vs. 2.7 h) and intraaortic balloon pump (15 vs. 8 h), and a higher ejection fraction before discharge from hospital, but none of these differences were significant. SECP appears to provide better myocardial performance early postoperatively, but lasting benefits were not apparent in this subset of patients with early revascularization. Because the IMA has a powerful effect on long term survival but is very difficult to use with antegrade SECP, we continue to favor the IMA without SECP in hemodynamically stable, young patients (less than 65 years) who are revascularized early after infarction.