We evaluated 249 patients (pts) with first acute myocardial infarction: 1. Pts without thrombolysis, n = 119, 2. Pts treated with thrombolysis within 6 hours following MI, n = 80 and 3. Pts treated with thrombolysis between 6-12 hours after MI. Arrhythmic events were evaluated during follow up. All underwent heart rate variability studies and coronary angiogram where anterograde flow (TIMI) and collateral flow (Rentrop scale 0-2 = poor collateral flow and 3 = good collateral flow) were determined. Pts in group 2 and 3 showed a better anterograde and collateral flow than group 1 (p < 0.001). A lower spectral power in the high frequency band and a higher ratio low/high frequency band were observed in group 1 (p < 0.05). Conjunctive consolidation analysis showed more malignant arrhythmias in TIMI 0-2 with poor collateral flow than TIMI 0-2 with good collateral flow (17/138-12.3% vs 0/14-0%). Kaplan Meier analysis was able to demonstrate more cardiac sudden death events in TIMI 0-2 with poor collateral flow than TIMI 0-2 with good collateral flow or TIMI 3 (x2 = 7.22, p = 0.028), independently of thrombolytic treatment.