Background: Although postoperative atrial fibrillation(AF) is one of the most frequent complications of coronary artery bypass graft(CABG) surgery, factors associated with the development of postoperative AF have been not clear. We sought to investigate the correlation between preoperative left ventricular diastolic function used by transthoracic echocardiography(TTE) and postoperative AF after CABG. Methods: Two hundred five patients (mean age 63 짹 10 years) undergoing elective isolated CABG were enrolled in this study. Routine TTE and tissue Doppler imaging(TDI) were performed before surgery. Postoperative AF was detected with continuous electrocardiography(EKG) monitoring throughout hospitalization. Results: Postoperative AF occurred in forty five of two hundred five patients (22%). Patients with postoperative AF were significantly older than patients without postoperative AF(69 짹 8 vs 62 짹 9 years, p<0.001). Compared with patients without postoperative AF, patients with postoperative AF had a significantly preoperative larger left atrial volume index(LAVI) (27.0 짹 10.2 vs 23.5 짹 8.0 ml/m2, p=0.015), a higher mitral early diastolic peak velocity(E) (68 짹 16 vs 62 짹 18 cm/s, p=0.028), and a higher mitral E/mitral annular early diastolic peak velocity(E���) ratio (15짹 5 vs 13 짹 5, p=0.031). By multivariate logistic regression analysis, only age (OR 1.09, 95% CI 1.04-1.15, p<0.001) and mitral E velocity (OR 1.05, 95% CI 1.01-1.08, p=0.001) were independent predictors of postoperative AF. Conclusions: This study suggests that assessment of preoperative left ventricular diastolic function used by TTE may be valuable in predicting postoperative AF after CABG. Keywords: Atrial fibrillation, coronary artery bypass graft surgery, diastolic function