ABSTRACT Introduction: Atrial fibrillation is the main complication in the postoperative period of cardiovascular surgery. Its genesis is multifactorial, so its rapid identification to mitigate the associated risks is essential. Objective: To evaluate the incidence of atrial fibrillation in patients undergoing coronary artery bypass grafting (CABG) and its relationship with other complications in our setting. Methods: This is a multicenter, observational study involving patients undergoing isolated CABG between 2017 and 2019 with data from the Registro Paulista de Cirurgia Cardiovascular (or REPLICCAR II). Variables were prospectively collected in REDCap following the definitions given by version 2.73 of the Society of Thoracic Surgeons Adult Cardiac Surgery Database. Data were collected with prior authorization from the local ethics committee and analyses performed in R software. Results: A total of 3,803 patients were included, of these 605 had postoperative atrial fibrillation (POAF). In order to adjust the groups, propensity score matching was used. Such analyses resulted in 605 patients in each group (without POAF vs. with POAF). Among patients with POAF, the mean age was 67.56 years, with a prevalence of males (73.6%, 445 patients). Patients belonging to the group with POAF had a mortality rate of 9.26% (P=0.007), longer ventilation time (P<0.001), pneumonia (P<0.001), and sepsis (P<0.001). In multiple analysis, acute renal dysfunction (P=0.032) and longer intensive care unit stay (P<0,001) were associated with the presence of POAF. Conclusion: POAF in CABG is associated with longer intensive care unit and hospital stay, as well as renal dysfunction, pneumonia, and in-hospital mortality. Introduction surgery multifactorial essential Objective (CABG setting Methods multicenter 201 or II. II . II) 273 2 73 2.7 Database software Results 3803 3 803 3,80 included 60 (POAF) groups used without vs POAF) 6756 67 56 67.5 years 73.6%, 736 6 (73.6% 44 patients. patients) 926 9 26 9.26 P=0.007, P0007 P P=0.007 , 0 007 (P=0.007) P<0.001, P0001 P<0.001 001 (P<0.001) P<0.001. analysis P=0.032 P0032 032 (P=0.032 P<0,001 (P<0,001 Conclusion inhospital 20 27 7 2. 380 80 3,8 (POAF 675 5 67. 73.6% (73.6 4 92 9.2 P000 P=0.00 00 (P=0.007 P<0.00 (P<0.001 P=0.03 P003 03 (P=0.03 P<0,00 (P<0,00 38 8 3, 73.6 (73. 9. P00 P=0.0 (P=0.00 P<0.0 (P<0.00 (P=0.0 P<0,0 (P<0,0 73. (73 P0 P=0. P<0. (P<0.0 (P=0. P<0, (P<0, (7 P=0 P<0 (P<0. (P=0 (P<0 ( P= P< (P= (P< (P