The success of thrombolytic therapy for acute myocardial infarction is limited by bleeding complications, the impossibility of reperfusing all occluded coronary arteries, recurrent myocardial ischemia, and the relatively small number of patients who are appropriate candidates for this therapy. We hypothesized that these problems could be overcome by the use of immediate percutaneous transluminal coronary angioplasty (PTCA), without previous thrombolytic therapy. At 12 clinical centers, 395 patients who presented within 12 hours of the onset of myocardial infarction were treated with intravenous heparin and aspirin and then randomly assigned to undergo immediate PTCA (without previous thrombolytic therapy, 195 patients) or to receive intravenous tissue plasminogen activator (t-PA, 200 patients) followed by conservative care. Radionuclide ventriculography was performed to assess ventricular function within 24 hours and at six weeks. Among the patients randomly assigned to PTCA, 90 percent underwent the procedure; the success rate was 97 percent, and no patient required emergency coronary-artery bypass surgery. The in-hospital mortality rates in the t-PA and PTCA groups were 6.5 and 2.6 percent, respectively (P = 0.06). In a post hoc analysis, the mortality rates in the subgroups classified as "not low risk" were 10.4 and 2.0 percent, respectively (P = 0.01). Reinfarction or death in the hospital occurred in 12.0 percent of the patients treated with t-PA and 5.1 percent of those treated with PTCA (P = 0.02). Intracranial bleeding occurred more frequently among patients who received t-PA than among those who underwent PTCA (2.0 vs. 0 percent, P = 0.05). The mean (+/- SD) ejection fractions at rest (53 +/- 13 vs. 53 +/- 13 percent) and during exercise (56 +/- 13 vs. 56 +/- 14 percent) were similar in the t-PA and PTCA groups at six weeks. By six months, reinfarction or death had occurred in 32 patients who received t-PA (16.8 percent) and 16 treated with PTCA (8.5 percent, P = 0.02). As compared with t-PA therapy for acute myocardial infarction, immediate PTCA reduced the combined occurrence of nonfatal reinfarction or death, was associated with a lower rate of intracranial hemorrhage, and resulted in similar left ventricular systolic function.