We analysed risk of cardiac arrest on the base of entry data (history and clinical examination) in group of 540 consecutive patients (pts) with acute myocardial infarction treated with thrombolytics. Arrest occurred in 82 (pts).We stated pts with arrest were significantly older (63.9±10.5 vs 58.9±10.7y, p<0.001), often had atrioventricular block II-III° (26.8 vs 10.0%, p<0.001), history of previous infarction (25.6 vs 13.1%) history of arterial hypertension (47.6 vs 33.4%, p<0.05). Entry systolic pressure was lower (122+36.5 vs 135+26.4mmHg, p<0.001) and Killip-Kimball class worse (1.4±0.7 vs 1.2±0.6, p<0.01) in pts who later had arrest. Time from onset of symptoms to admission was equal in both groups (2.94h).No significant differences in gender (men - 64.6 vs 72.5% NS), site of infarction (anterior - 41.5 vs 44.85, NS), history of smoking (52.4 vs 59.4%, NS), history of diabetes (14.6 vs 13.1%, NS) were observed. Pts with a-v block had predominantly ventricular fibrillation. Pts with hypertension and first anterior infarction had typically electromechanical dissociation because of pericardial tamponade.Conclusions: Factors of high risk of cardiac arrest during infarction are: old age, high Killip class, low systolic pressure, atrioventricular block (relative risk 2.0), history of previous infarction (risk 2.0), history of hypertension (risk 1.6)