INTRODUCTION: Despite the latest innovations in surgical and cardiopulmonary bypass techniques, atrial fibrillation remains a common occurrence in patients undergoing heart surgery, and has been shown to increase the incidence of intra- and postoperative complications. For this reason, it is among the top 10 research topics in cardiovascular surgery. METHOD: Observational, analytical, retrospective study carried out at the largest cardiovascular centre in Mexico. Adult patients (>
18 years) with no history of atrial fibrillation who underwent on-pump heart surgery between 1 January 2022 and 31 December 2023 were included. Variables that have previously been correlated with postoperative atrial fibrillation (POAF) were evaluated. RESULTS: A total of 544 patients were included. The incidence of POAF was 23.8%. Overall in-hospital mortality was 5.9%. There was a significant difference in age between patients that developed postoperative atrial fibrillation and those that maintained sinus rhythm (62 years vs 57 years, p = <
0.01). Using a univariate logistic regression model, we found that POAF significantly predicts the occurrence of hospital-acquired pneumonia (OR 3.12, 95% CI 1.61-6.02, p = <
0.01) and the requirement for renal replacement therapy (OR 3.04, 95% CI 1.34-6.86, p = <
0.01). CONCLUSIONS: Atrial fibrillation is a common arrhythmia in the postoperative period of on-pump heart surgery, and is a predictor of adverse outcomes. Prevention, early detection and treatment of POAF may have prognostic implications.