To evaluate the benefit of emergency coronary angioplasty (PTCA) among patients with acute myocardial infarction having patent infarct-related arteries, we investigated 104 patients who received thrombolysis and/or PTCA within 24 hrs after onset of symptoms. The morphology of coronary artery lesions was qualitatively assessed by angiography and categorized as symmetrical or asymmetrical narrowing with smooth margins (S-group, 72 cases) and asymmetrical narrowing in the form of convex intraluminal obstruction representing a thrombus (T-group, 32 cases). Soon after intervention, angiographic success (residual stenosis less than 75%) was achieved in 85% with PTCA (92% in the T-group vs 82% in the S-group) and in 29% without PTCA (53% vs 16%). At hospital discharge, the figures were 82% with PTCA (75% vs 87%) and 43% without PTCA (73% vs 30%). The incidence of re-infarction and/or total occlusion of the infarct-related artery was 9% with PTCA in both the T- and S-groups but 26% in those without PTCA (6% in the T-group vs 31% in the S-group). These data suggest that in patients with patient infarct-related arteries and severe original stenosis, PTCA has an advantage over thrombolysis alone. Qualitative analysis of coronary morphology by angiography provides a framework for selecting adequate therapy.