Abstract: Objective: To study the correlation between atrial fibrillation(AF) in acute myocardial infarction(AMI) and coronary lesions.Methods: Eighteen patients who developed AF after the onset of AMI were classified into AF group and 20 patients who did not develop AF after the onset of AMI were classified into non-AF group.According to the onset time of AF,AF group was divided into two subgroups:subgroup A(n=8,AF developed within 24 hours after the onset of AMI)and subgroup B(n=10,AF developed>24 hours after the onset of AMI).The angiographic outcome was compared between the two groups and the two subgroups.Results: The incidence of multivessel disease was significantly higher in AF group than in non-AF group(P<0.05).Occlusion of the right proximal coronary artery was responsible for AMI in subgroup A,while occlusion of the left anterior descending branch was responsible for AMI in subgroup B(P<0.05).Conclusions: The patients who developed AF in the course of MI demonstrates severer coronary lesion.The onset time of AF in AMI is related to the location of the infarct-related coronary lesions.