The effect of perfusion of the infarct artery on myocardial infarct size was studied in 39 patients who had not received interventive therapy. At predischarge coronary angiography, 19 patients had subtotal and 20 total occlusion of the infarct artery. The early ST-segment elevation recorded on a 12-lead electrocardiogram was used as an index of the amount of initially jeopardized myocardium. Infarct size was estimated by peak serum creatine kinase and, at discharge, by a QRS score, sigma Q and sigma R on a 12-lead electrocardiogram, and by radionuclide global and infarct segment left ventricular ejection fraction. Despite a similar degree of initial ischemia (sigma ST), infarct size was smaller in the 11 patients with anterior infarction and subtotal occlusion than in the 9 patients with anterior infarction and total occlusion when measured by peak serum creatine kinase (2114 +/- 1192 U/l vs. 3653 +/- 1059 U/l, p less than 0.02), QRS score (5.0 +/- 2.7 vs. 9.6 +/- 3.5, p less than 0.01), sigma Q (3.25 +/- 2.74 mV vs. 5.92 +/- 3.56 mV, p less than 0.10), sigma R (4.36 +/- 1.25 mV vs. 2.16 +/- 0.91 mV, p less than 0.001), global left ventricular ejection fraction (45.0 +/- 12.2% vs. 33.4 +/- 6.7%, p less than 0.05), and infarct segment ejection fraction (40.4 +/- 8.2% vs. 30.3 +/- 5.4%, p less than 0.05). In the inferior infarct patients, both the degree of initial ischemia and final infarct size were similar in the 8 patients with subtotal and in the 11 patients with total occlusion.(ABSTRACT TRUNCATED AT 250 WORDS)