A multicenter randomized trial of anisoylated plasminogen streptokinase activator complex (APSAC) versus heparin in patients with acute myocardial infarction of less than 4 hours' duration was undertaken in 19 hospitals. Of the 313 patients, 151 received heparin and 162 APSAC (30 U as intravenous injection). Within 28 days of hospital stay, 19 deaths (12.6%) occurred in the heparin group and 9 deaths (5.6%) in the APSAC group (p = 0.032). After 24 hours, patients in the APSAC group had a significantly lower incidence of cardiogenic shock (3.2 vs 9.5%, p = 0.031), asystole (3.8 vs 10.8%, p = 0.015) and need for resuscitation (5.1 vs 11.5%, p = 0.039). There was no difference in global and infarct-related ejection fraction between the 2 groups. Thus, APSAC favorably influences prognosis and clinical course in hospital.