Coronary arteriography was performed 16 +/- 3 days (range 7 to 21 days) in 106 patients with acute transmural myocardial infarction (61 posterior infarct, 45 anterior infarct). Coronary arteriography was performed without serious complications. Only 44% of patients with anterior infarct had total occlusion of the left anterior descending artery while a significant stenosis of the vessel was observed in the others -27% had a single vessel disease, 49% had two lesions and 22% had three lesions; one patient had angiographically normal coronary arteries. Among the patients with posterior infarction, 21% had one vessel disease and double or triple lesions accounted for 39% of each. Sixty per cent of patients with anterior infarction and 45% with posterior infarction had no collateral vessels. In the others patients collateral circulation had a protective effect only in anterior infarction. Age has no effect on the distribution and number of lesions nor on the development of a collateral circulation. The location and severity of the lesions were not different in patients who presented with arrythmias and those who did not.