Objective To analyze predictive demographic and perioperative variables of postoperative atrial fibrillation in patients who underwent exclusively coronary artery bypass grafting.Methods This was a retrospective cohort. We randomly selected 105 medical records of patients who underwent exclusively coronary artery bypass grafting in 2014. Demographic, clinical (preoperative and immediate postoperative) data and related with surgical procedure were collected from medical records. The occurrence of postoperative atrial fibrillation was considered until the third day after the surgery. Variables were analyzed using descriptive and inferential statistics. To identify predictive factors of postoperative atrial fibrillation we used a decision tree model with Classification and Regression Trees algorithm.Results Atrial fibrillation incidence was 19.0% (n=20). Patients with left atrial >40.5mm and aged >64.5 years were more likely to develop the arrhythmia during the post-surgical period.Conclusion Left atrial diameter and advanced age were predictive factors of atrial fibrillation in patients who underwent exclusively coronary artery bypass grafting.