To evaluate the effects of late thrombolysis on left ventricular volume and function in acute myocardial infarction, two-dimensional echocardiography and radionuclide angiography were performed before discharge and after 1 year of follow-up study in 34 patients with acute anterior myocardial infarction. Of these, 10 admitted to the coronary care unit within 4 h from the onset of symptoms were treated with recombinant tissue-type plasminogen activator (rt-PA) (Group A) and 24 admitted between 4 and 8 h after onset were randomly assigned to receive either rt-PA (Group B, n = 12) or conventional therapy (Group C, n = 12). Seven to 10 days after admission, all patients underwent cardiac catheterization and coronary angiography. Patency of the infarct-related vessel was 70% in Group A, 66% in Group B and 33% in Group C and the average Thrombolysis in Myocardial Infarction (TIMI) coronary perfusion grade was 1.9 +/- 0.8 for Group A, 1.6 +/- 1.0 for Group B and 0.84 +/- 0.95 for Group C (Group A versus Group C p less than 0.01; Group B versus Group C p less than 0.05). At predischarge evaluation, mean left ventricular end-systolic and end-diastolic volumes were higher in Group C than in Group B (p less than 0.001 and 0.05, respectively) and Group A (p less than 0.005 for both); mean left ventricular ejection fraction at rest was lower in Group C than in Group B and Group A (p less than 0.05 for both). At 1 year follow-up study, end-systolic and end-diastolic volumes remained higher in Group C than in Group B (p less than 0.05 for both) and Group A (p less than 0.005 for end-systolic volume and p less than 0.001 for end-diastolic volume); ejection fraction at rest was lower in Group C than in Groups A and B (p less than 0.05 for both); during exercise, it increased more in Group A than in Group C (p less than 0.01). Comparison of data obtained before discharge and at the 1 year follow-up study revealed a significant differences in end-systolic volume (p less than 0.05) in Group C patients and in end-diastolic volume in patients in Groups B (p less than 0.05) and C (p less than 0.001). The beneficial effect of late thrombolysis with rt-PA may be related to a reduction in myocardial expansion and thus to a favorable influence on postinfarction left ventricular remodeling.