Aims Recent studies suggest an association between epicardial adipose tissue (EAT) and atrial fibrillation. The aim of the study is to evaluate the quantitative and qualitative characteristics of EAT in relation to atrial fibrillation burden after coronary artery bypass graft (CABG).Methods This prospective single-centre study included patients undergoing CABG. The patients underwent transthoracic echocardiography and collection of a bioptic sample containing right appendage and EAT during CABG for histological characterization. After surgery, clinical and telemetry data were collected.Results Fifty-six consecutive patients were enrolled. The mean postsurgical hospitalization was 7.9 W 3.7 days. Twenty-two patients had at least one episode of atrial fibrillation. In the atrial fibrillation group, there was a bigger atrial volume, a higher degree of diastolic disfunction, a thicker layer of EAT and an older median age in comparison with the group that did not develop it. EAT with a cut-off of 4 mm was a predictor of atrial fibrillation with an odds ratio (OR) of 1.49 (confidence interval (CI) 1.09-2.04), 73% of sensibility and 89% of specificity. From the histological analyses, the patients with atrial fibrillation had a significantly higher percentage of fibrosis. At univariate analysis, atrial volume [OR 1.05, CI 1.01-1.09, P U 0.022], E/A rate (OR 0.04, CI 0.02-0.72 P U 0.29), the percentage of fibrosis (OR 1.12, CI 1.00-1.25, P U 0.045) and age (OR 1.17, CI 1.07-1.28, P U 0.001) were predictors of atrial fibrillation. At multivariate analysis, atrial volume (P U 0.027), fibrosis (P U 0.003) and age (P U 0.039) were independent predictors of atrial fibrillation. ConclusionPostcardiac surgical atrial fibrillation is frequent. EAT thickness, atrial volume, fibrosis and age are predictors of postcardiac surgical atrial fibrillation.