Background. The impact of thrombolytic therapy on the incidence of complex ventricular arrhythmias is not yet clarified. The aim of this study was to investigate the impact of thrombolytic therapy on the incidence of complex ventricular arrhythmias, as well as long term association between complex ventricular arrhythmias and left ventricular remodelling, and their impact on five-year lethality. Methods. Ninety seven consecutive patients with first acute myocardial infarction (streptokinase was administered in 58 patients) underwent 24-hours Holter monitoring at discharge. Ventricular arrhythmias were classified according to Lown classification, and patients were grouped into the group with simple ventricular arrhythmias (Lown class 0 to 2), and the group with complex ventricular arrhythmias (Lown class 3 to 5). Echocardiography was performed at discharge, and six and twelve months after the infarction. Left ventricular volume indexes and ejection fraction was determined using Simpson's biplane formula. Results. In patients with complex ventricular arrhythmias left ventricular volume indexes were higher and ejection fraction was lower throughout the study, whereas wall motion score index was higher one year after the infarction. On the other hand, these variables were similar throughout the follow-up within the groups of patients with and without complex ventricular arrhythmias who received thrombolytic therapy. The incidence of complex ventricular arrhythmias was similar in thrombolysed and non-thrombolysed patients (11/58 vs. 5/39). There was no difference in five year lethality between patients with and without complex ventricular arrhythmias (4/16 vs. 13/81 patients). Conclusion. Our data indicated that left ventricular remodelling in patients with complex ventricular arrhythmias was not progressive after hospital discharge. The presence of complex ventricular arrhythmias was not associated with the increased five-year lethality, despite of more pronounced left ventricular remodelling. It occured that thrombolysis per se had no influence on the incidence of complex ventricular arrhythmias in the late hospital phase after the first acute myocardial infarction.