The hearts of 52 patients (aged 61 +/- 11 years, 34 men) who participated in the Thrombolysis in Myocardial Infarction (TIMI) Study and died from 5 hours to 260 days (median 2.7 days) after onset of chest pain were studied. One heart became available at cardiac transplantation. Of the 52 patients, 38 received recombinant tissue plasminogen activator (rt-PA) not followed by percutaneous transluminal coronary angioplasty (PTCA) or coronary artery bypass grafting (CABG). Eight had PTCA, and 6 had CABG. The infarcts were hemorrhagic by gross inspection (with histologic confirmation) in 23 patients, nonhemorrhagic in 20, not visible grossly in 2 and, in 7, there was no myocardial necrosis by either gross or histologic examination.(ABSTRACT TRUNCATED AT 250 WORDS)