The results of immediate percutaneous transluminal coronary angioplasty (PTCA) (260 +/- 167 minutes after onset of pain and an average of 56 minutes after thrombolysis) and deferred PTCA (average 9.6 days, range 1 to 30 days after infarction) were compared in 118 consecutive patients with acute myocardial infarction. The overall primary success rate of PTCA was 82.2 per cent; it was higher in those patients undergoing deferred angioplasty (96% vs 78%; p less than 0.05). The primary success rate of immediate PTCA was related to the severity of the stenosis before dilatation: 75 per cent success in occluded compared to 84 per cent in suboccluded vessels (over 90% stenosis) and 100 per cent success in vessels with under 90 per cent stenosis. Eighty one per cent of failed angioplasties occurred in patients with occluded arteries, the majority being left anterior descending (LAD) arteries (71.4%). The incidence of restenosis was 13.4 per cent. This complication was diagnosed at coronary arteriography performed 40 days after PTCA in 1 case, 47 days after PTCA in another case and at the 6 month control in 11 cases. Reocclusion was observed in 21 patients (21.7% of immediate successes). The occlusion was diagnosed at the first control after an average of 8 days in 15 cases. The interval between the onset of pain and thrombolysis and dilatation was significantly longer in the group with reocclusion compared with patients without reocclusion (314 minutes vs 193 minutes for thrombolysis, p less than 0.01; and 356 minutes vs 204 minutes fort PTCA, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)