Background: Atrial fibrillation(AF) is characterized by loss of atrial contraction, inadequate rapid ventricular response, and atrial overloading leading to elevated plasma natriuretic peptide. We compared the atrial mechanical function of patients whose rhythm was converted to sinus rhythm with patients whose rhythm was not converted to sinus rhythm after Maze procedure and evaluated whether the atrial mechanical function in the immediate post-operative states could predict conversion of AF to sinus rhythm. Methods: We prospectively reviewed 80 patients with AF who undergone Maze procedure from Feb 2005 to Jan 2007. We assessed mechanical function of the left atrium before,immediately after the procrdure, 6 and 12 months after the procedure and reviewed the clinical characteristics and plasma N-terminal pro-brain natriuretic peptide(NT-proBNP) levels before the procedure. Atrial mechanical function was assessed by means of left atrial ejection volume(LAEV) and left atrial ejection fraction(LAEF) with the prolate ellipse method during echocardiography. Results: Of 80 patients, 71 were patients whose rhythm was converted to sinus rhythm after Maze procedure(group 1), 9 were patients whose rhythm was not converted to sinus rhythm after the procedure(group 2). NT-proBNP levels were 1817짹3622 pg/ml in group 1 and 1250짹903 pg/ml in group 2(p=ns). Change in LAEV was 1.57짹15.10 ml, change in LAEF was 5.54짹9.20 % in group 1. Change in LAEV was -18.50짹16.71 ml, change in LAEF was -3.27짹5.05 % in group 2. There were no significant differences in age, sex, smoking, hypertension, diabetes mellitus, stroke, thyroid dysfunction, renal failure, initial NT-proBNP levels between the two groups. Immediate postoperative LAEV(p=0.381)and LAEF(p=0.238) did not predict recovery of AF to sinus rhythm. During follow-up, LAEV(p=0.001) and LAEF(p=0.006) was significantly improved in group 1 compared with group 2. Conclusions: Irrespective of presenting clinical characteristics, initial NT-proBNP levels and initial atrial mechanical function, atrial mechanical function recovered in patients whose rhythm was converted to sinus rhythm after Maze procedure in contrast with patients whose rhythm was not converted to sinus rhythm.