Autopsy findings are reported for 6 patients who died early (8, 9, 12, 13 and 14 days) or late (52 days) after combined thrombolysis and percutaneous transluminal coronary angioplasty (PTCA) for acute myocardial infarction. Morphologic changes in the coronary arteries at the site of revascularization included injury to the inner portion of the arterial wall (intimal splitting, subintimal dissection, medial tears and submedial dissection) and necrosis of medial smooth muscle cells. Residual mural thrombi and thrombotic reocclusion were noted within the arterial lumen. There was a beginning neointima formation in all patients who died early and a reobstructing neointima proliferation in the patient who died late after PTCA. The results of this study support the suggestion that both rupture and dissection of the inner arterial wall and necrosis of the tunica media resulting from irreversible dilatation of the grossly intact outer layers are the most important mechanisms of PTCA. Response to arterial wall injury after PTCA is a neointima formation leading to covering of mural thrombi and thrombogenic intimal, medial and adventitial substances and smoothing of the luminal surface. Large residual mural thrombi and excessive neointimal proliferation may cause restenosis within a few weeks.