Background: It has been reported that catheter ablation (CA) significantly improves left ventricular (LV) function and causes reverse remodeling of the left atrium (LA) in atrial fibrillation (AF). But, there are few studies comparing echocardiographic heart function between CA and antiarrhythmic treatments (AT) for AF. Methods: We conducted a non-randomized prospective comparison of the 2 treatment strategies in patients with AF. A total of 42 patients with drug-resistant (1 or more antiarrhythmic drugs) AF underwent CA, and 30 patients who refused CA continued medical treatments. Transthoracic echocardiography (TTE) was performed to evaluate LV ejection fraction (EF), chamber size and LV mass index. Maintenance of sinus rhythm was determined by clinical interview, 48-hour ambulatory electrocardiographic monitoring and event recording. Results: 1. Sinus rhythm maintenance was significantly higher in patients with CA than in AT group (35 patients (83.3%) vs 17 patients (56.7%), p=0.02). 2. LVEF increased significantly (55.9짹7.0% vs 59.6짹5.9%, p<0.01), while LA diameter and LA volume index decreased significantly (42.0짹5.4mm vs 40.6짹5.5mm, p=0.02, 38.2짹8.7mL/m2 vs 35.3짹8.0mL/m2, p=0.01, respectively) in patients with CA. Also, LV mass and LV mass index were decreased from 190.5짹36.1g to 179.3짹32.4g (p=0.02) and from 104.2짹20.5g/m2 to 98.2짹18.3g/m2 (p=0.03), respectively. In patients with AT, there were no significant change in the above echocardiographic parameters over a mean follow-up period of 20.7짹7.5 months. There was no significant difference in blood pressure, use of angiotensin converting enzyme inhibitor or angiotensin receptor blocker between the two groups. Conclusions: Besides improved systolic heart function and reverse remodeling of LA, LV mass was significantly decreased after CA of AF compared with AT. Our results suggest that aggressive rhythm management could result in reverse remodeling of the left ventricle.