Postoperative atrial fibrillation (POAF) is a common complication after cardiac surgery, marked by an irregular and rapid heart rate, and associated with increased morbidity, longer hospital stays, and higher costs. Its complex pathophysiology involves atrial remodeling, inflammation, and autonomic dysregulation. Surgical trauma and cardiopulmonary bypass trigger an inflammatory response, releasing cytokines. Epicardial fat around the heart secretes pro-inflammatory cytokines, and its increased thickness is linked to higher inflammation and atrial fibrillation. This study uses RNA sequencing (RNA-seq) to profile gene expression in epicardial fat, identifying key genes involved in inflammation and metabolism. By comparing patients with and without POAF, RNA-seq reveals differentially expressed genes associated with postoperative atrial fibrillation.