Background No single randomized study has ever before addressed the safety of On-Pump coronary artery bypass grafting (CABG) vs Off-Pump CABG in the setting of atrial fibrillation (AF) and data from small observational samples remain inconclusive. Methods and findings Procedural data from KROK (Polish National Registry of Cardiac Surgery Procedures) were retrospectively collected. Of initial 188,972 patients undergoing CABG, 7,913 presented with baseline AF (76.0% men, mean age 69.1±8.2) and underwent CABG without concomitant valve surgery between 2006-2019 in 37 reference centers across Poland. Mean followup was 4.7±3.5 years (median 4.3 IQR 1.7-7.4). Cox proportional hazards models were used for computations. Of included patients, 3,681 underwent On-Pump-(46.52%) as