The aim of this study was to assess ventricular arrhythmias after intravenous thrombolysis for acute myocardial infarction and to determine their relationship with coronary artery patency. A 24 hour Holter recording was started 3.1 +/- 0.2 hours after the onset of pain in 40 patients (age 54 +/- 1.6 years, 42.5% anterior infarcts) treated by streptokinase (42.5%) or tissue plasminogen activator (57.5%) within 3.3 +/- 0.2 hours of the beginning of symptoms. The arrhythmias were analysed on a Marquette 8000 computer. Coronary angiography was systematic and was performed 26.7 +/- 2.5 hours (within 4 hours in 60% of patients) after the onset of pain to define coronary artery patency (TIMI 2 and 3: 72.5%) or occlusion (TIMI 0 or 1: 27.5%). Ventricular arrhythmias were common and generally well tolerated (one defibrillation for ventricular fibrillation). Accelerated idioventricular rhythms and ventricular tachycardias were equally prevalent in patients with patent arteries (90% and 83%) as with occluded arteries (82% and 73%). The prevalence of sustained ventricular tachycardias (> 15 complexes) and of early accelerated idioventricular rhythms (< or = 6 hours) was significantly higher in patients with patent coronary arteries: 38% versus 0% (p < 0.05) and 76% versus 18% (p < 0.01). These arrhythmias may be considered to be non-invasive markers of early coronary reperfusion, with a sensitivity of 38 and 76% and a specificity of 100 and 82%. Coronary patency was associated with higher numbers of ventricular extrasystoles, ventricular tachycardias and accelerated idioventricular rhythms by a factor of 14, 13 and 32 respectively.(ABSTRACT TRUNCATED AT 250 WORDS)