Of 150 consecutive patients with acute myocardial infarction transported by helicopter for acute intervention, 55 had intravenous thrombolytic therapy (tissue plasminogen activator in 12, streptokinase in 43) initiated prior to transfer. Patients were transported 55 +/- 10 ground miles in 17 +/- 6 minutes and no patient died or experienced bleeding or hemodynamic instability during transfer. Patients receiving thrombolytic therapy had a higher incidence of arrhythmias during transit compared to the untreated group, ventricular tachycardia in six and third-degree atrioventricular block in one compared to ventricular tachycardia in one patient, respectively (p = 0.005). However, these arrhythmias were transient and did not require cardioversion, temporary pacing, or further antiarrhythmic medical treatment. Chest pain was relieved or decreased more frequently in the patients receiving thrombolytic therapy vs. those untreated; 21 of 55 vs. 21 of 95 respectively (p = 0.04). Immediate coronary angiography confirmed a higher incidence and more complete infarct vessel patency (34/55 vs. 30/95) in the patients receiving tissue plasminogen activator or streptokinase (p less than 0.001). Thus, helicopter transfer of patients with evolving myocardial infarction is safe, and early initiation of thrombolytic therapy is associated with increased infarct vessel patency and benign reperfusion arrhythmias.