Objective To explore the characteristics and risk factors of ventricular fibrillation(Vf) in open-chest acute myocardial infarction models of swine.Methods Coronary artery was surgically occluded at different percentage point of LAD varying from 25% to 75% in fifty-seven miniswines.Cardiac fraction(LVEF) using echocardiography was assessed before and 1 hour after myocardial infarction(MI).Coronary angiography was used to confirm the position of ligation after MI.The weight,gender,heart rate(HR) before and after MI,LVEF,thoracotomy route(intercostal or parasternal),operation duration,percentage point of LAD ligation,arhythmia after MI were recorded and compared between Vf group and Vf-free group.The risk factors of Vf were determined by logistic regression analysis.Results Eighteen of the 57 pigs suffered from ventricular fibrillation within 35 min after LAD ligation and 11 cases died.Compared with Vf-free group,the Vf group featured a higher position of LAD ligation,a higher incidence of ventricular tachycardia and maximal HR>160 bpm post MI.Logistic regression analysis showed the position of LAD ligation was a sole risk factors of Vf after MI with a statistical significance.Pigs with HR>160 bpm or <60 bpm post MI was susceptible to Vf.Conclusion The position of LAD ligation is a vital determinant of Vf in establishing acute MI model of swine.Attentions should be paid to the first 30 min after LAD ligation,HR,and ventricular tachycardia.