Background: Atrial fibrillation (AF) is a frequent and serious complication of coronary artery bypass graft (CABG) surgery. Methods: We undertook a retrospective review of the records of patients undergoing CABG at Imam Ali Hospital between February 1, 2003 and February 1, 2006. The patients were divided in two groups, ie, Group A (AF) and Group B (no AF). The association between the occurrence of AF following CABG and other variables was compared with respect to continuous or categorical variables by t-test and c2-test. Results: Multivariate logistic regression analysis of potentially predictive factors in univariate analysis showed that opium use, type of operation, and crossclamp time were predictors of AF following CABG. Conclusion: This study identifies some new predictors of postoperative AF, control of which could lead to a lower incidence of AF and reduced morbidity, mortality, and resource utilization for patients undergoing cardiac surgery.