Thrombolysis reduces mortality in patients with acute myocardial infarction (AMI) who are hospitalized within 6 hours from the onset of symptoms. AMIs involving a small area of myocardium show a lower mortality in comparison with AMI involving a large area. The present study was aimed at evaluating the safety and efficacy of rescue thrombolysis in patients with large AMI who had failed thrombolysis. Ninety patients (69 Males and 21 Females), mean age 56.7 +/- 9 years, hospitalized for suspected AMI within 4 hours from the onset of symptoms, suitable for thrombolysis (First episode), and showing pain and persistent ST segment elevation 120 minutes after starting thrombolysis, were randomized (double-blind) into two groups. Group A (45 patients: 10 females and 35 males) received an additional thrombolytic treatment (rTPA 50 mg), 10 mg as bolus plus 40 mg in 60 minutes. Group B (45 patients: 11 females and 34 males) received placebo. Positive noninvasive markers were defined as follows: (1) resolution of chest pain, (2) > or = 50% reduction in ST segment elevation, (3) double marker of creatine kinase (CK) and CK-MB activity 2 hours after the start of thrombolysis, and (4) occurrence of reperfusion arrhythmias within the first 120 minutes of thrombolytic therapy. Blood pressure, heart rate, and ECG were continuously monitored. An echocardiogram was carried out at entry, and before discharge, to control ejection fraction and segmentary kinetics. Adverse events such as death, re-AMI, recurrent angina, incidence of major and minor bleeding, and emergency CABG/PTCA were checked. The groups were similar in terms of age, sex, diabetes, smoking habits, hypertension, and adjuvant therapy (beta-blockers). No significant difference was observed between the two groups regarding the time elapsed from the onset of symptoms to thrombolysis and AMI localization. Thirty-five patients (77.7%) showed reperfusion (10-50 minutes) after commencement of additional rTPA. Of the patients receiving placebo, 12 (26.6%) showed reperfusion within 35-85 minutes. Group A showed an earlier and lower CK and CK-MB peak than the control group, (respectively, p = 0.0001-0.009 and 0.002). Mortality (17.7%, 16 patients) was higher in group B than in the additional rTPA group, i.e., 6.6% (3 patients) in group A versus 28.8% (13 patients) in Group B (p = 0.041). Seven patients from group A showed nonfatal re-AMI. Angina was observed in 18 patients (40%) from group A and 3 (6.6%) from group B (p = 0.006). Ten of these patients underwent urgent PTCA (9 from group A and 1 from group B), and 3 from group A underwent urgent CABG. Minor bleeding was higher in group A than in group B (44.4% versus 15.5%, p = 0.047). Major bleeding was observed in group A (nonfatal stroke). At predischarge, the echocardiogram ejection fraction was higher in group A than in group B (46 +/- 8% versus 38 +/- 7%, p = 0.0001). Our data suggest that an additional dose of thrombolytic drug in patients with unsuccessful thrombolysis is feasible and also that the bleeding increase is an acceptable risk in comparison with the advantages obtained in reducing AMI extension. Rescue thrombolysis can allow a gain in time to perform mechanical revascularization in patients admitted to hospital without an interventionist cardiology laboratory or in those who have to be referred to another hospital for urgent CABG.