In 29 patients with evolving acute myocardial infarction, acute reperfusion of the infarct-related coronary artery was attempted using percutaneous transluminal coronary angioplasty (PTCA). Before PTCA, angiography showed 23 totally occluded and 6 severely stenotic infarct-related coronary arteries. PTCA was initially successful in 25 of 29 patients (86%). Reocclusion occurred in 4 patients within 12 hours after successful PTCA and was associated with new electrocardiographic changes or recurrence of symptoms. In 17 patients the infarct-related coronary artery remained patent at early follow-up; late stenosis occurred in 4 patients. Recurrence of stenosis was accompanied by development of angina. No clinical or angiographic features distinguished those with ultimate vessel patency, occlusion or recurrence of stenosis. On follow-up, ventricular function appeared better preserved or improved in those with a patent infarct-related coronary artery than in those with an occluded infarct-related coronary artery. Further studies are warranted to compare PTCA and streptokinase as primary reperfusion modalities in evolving acute myocardial infarction.