The correlation between progression of atherosclerotic lesions and the compensatory development of collaterals which prevent ischemic events, particularly myocardial infarction, were examined in patients who underwent repeated coronary angiography (CAG) after medical therapy. Twenty-five patients with lesions in their coronary arteries perfusing the viable myocardium during the first study, which progressed to total occlusion in the second study, were evaluated. The subjects' mean age was 55.1 years, and the mean time interval between the two studies was 44.1 months. CAG was performed in the chronic stage of myocardial infarction or the stable phase of angina pectoris, but three patients underwent repeated CAG studies during the acute phase of myocardial infarction. The percent diameter of the narrowing in the lesion was assessed according to the AHA system. Concerning the sites of lesions with progression to complete occlusion, 14 (56%) were located in the proximal segment of the left anterior descending artery (segment 6 or 7), and six lesions were in the main trunk of the right coronary artery (segment 1, 2 or 3). In 11 patients with stable angina, associated lesions showed progression from 90 or 99% stenosis to complete occlusion. Seven patients with lesions exhibiting 99% stenosis had collaterals, and four patients with lesions exhibiting 90% stenosis had no collaterals during the first study. However, good collaterals were demonstrated in all patients in the second study. Seven patients had episodes of newly developed unstable angina. The lesions in five of the seven patients progressed from 75% or 90% stenosis to complete occlusion, and in one patient with triple vessel disease the lesion progressed from 99% stenosis to complete occlusion in the second study. The former five patients did not have collaterals in the first study, but development of collaterals was demonstrated in all seven patients in the second study. Seven patients had episodes of myocardial infarction, and in six of these, the lesions progressed from 75% or less stenosis to complete occlusion.(ABSTRACT TRUNCATED AT 400 WORDS)