With the increasing use of thrombolytic therapy, the presence and time course of reperfusion-induced ventricular arrhythmias and ST-segment changes have become of particular interest. Technical improvements in bipolar Holter monitoring offer the opportunity to record both parameters continuously and simultaneously. Time course and interaction of both parameters in dependence on the onset of thrombolysis and time of reperfusion were investigated in 30 patients with acute myocardial infarction. Reperfusion was achieved in 20 patients after 49 +/- 23 minutes and in another 2 patients after 120 minutes (73%, group A). Vascular occlusion persisted in 8 patients for greater than 24 hours (group B). Sudden ST-segment changes (greater than 0.2 mV/15 min) in the bipolar leads indicated reperfusion in 7 of 22 patients (32%). Idioventricular rhythms, most frequent in reperfused patients (group A: 18 of 22 patients, mean 121 beats/hour), were unspecific reperfusion markers (group B: 5 of 8 patients, 1 beat/hour) unless frequent (p less than 0.05) or longer lasting, repetitive (p less than 0.01) episodes were considered. Premature ventricular beats and couplets (p less than 0.05) were also most frequent in group A (peak frequency 3 to 5 hours after thrombolysis). Ventricular tachycardia observed in 21 of 22 patients (95%) in group A and in 3 of 8 (38%) in group B (p less than 0.01) attained their peak frequency 7 to 9 hours after thrombolysis. They occurred most often in anterior myocardial infarction and were often preceded by frequent singular premature beats (r = 0.78).(ABSTRACT TRUNCATED AT 250 WORDS)