Successful percutaneous transluminal coronary angioplasty (PTCA) was performed during evolving acute myocardial infarction (AMI) in 41 patients. Catheterization was performed within 1 hour of presentation, from 1 to 12 hours (mean 3.3) following symptom onset. In 17 of 29 patients with a totally occluded coronary artery, successful thrombolytic therapy was followed by PTCA of a residual high-grade atheromatous stenosis. Successful PTCA without prior thrombolytic therapy was employed in 11 of 12 subtotal coronary stenoses producing acute infarction syndromes and in two patients having critical coronary stenoses not immediately responsible for AMI. Three patients experienced early in-hospital reocclusion with reinfarction. One death occurred in a patient presenting with cardiogenic shock. All remaining patients had prompt pain relief, subsequent stable clinical courses, and no clinical or late angiographic evidence of coronary reocclusion. Dramatic improvement of regional and global left ventricular function was evident in 22 of 27 patients undergoing late left ventricular angiography. At follow-up, 94% of patients remained free of angina although three required repeat dilatation of recurrent stenoses. We concluded that PTCA may be performed with or without thrombolytic therapy in selected patients with AMI and may reduce the likelihood of late reocclusion following successful thrombolytic therapy.