Background: We prospectively evaluated the effect of sinus rhythm restoration and reversibility of left ventricular (LV) function by catheter ablation in patients with atrial fibrillation (AF) and depressed LV function. Methods: Of 181 patients who underwent catheter ablation of drug-refractory AF, 17 patients (9.4%) with paroxysmal (n=8) and persistent (n=9) AF who had LV ejection fraction (EF) of less than 40% despite optimal medical therapy were included in this study. None had significant structural heart diseases. We selected as controls 48 patients without LV dysfunction who matched according to age, sex, and classification of AF. All patients underwent anatomical left atrial ablation combining electrical isolation of all pulmonary veins. We determined the effect of AF suppression and improvement in LV function with Holter and echocardiographic examinations at regular basis of interval. Results: At a mean follow up of 32.8짹7.8 months after AF ablation, 78% of the patients with depressed LVEF and 86% of the controls remained in sinus rhythm (P=0.27). Before the ablation, average heart rate in patients with depressed LVEF was not significantly different from that in controls (72.8짹11.6 bpm vs. 67.3짹12.5 bpm, P=0.195). The patients with depressed LVEF had significant improvement in LV function including EF (28.6짹8.5% vs. 50.1짹10.8%, P<0.001) and LV systolic dimension (40.0짹8.1 mm vs. 32.2짹7.8 mm P=0.023) compared to those of pre-ablation. However, LV diastolic dimensions was not significantly changed (53.2짹6.4 mm vs. 51.6짹6.7 mm, P=0.374). Conclusions: In patients with AF and depressed LV function, efficacy of catheter ablation was comparable to patients with normal LV function. Restoration and maintenance of sinus rhythm by AF ablation significantly improved LV function with shortening of systolic dimension, but no change in diastolic dimension. Catheter ablation without use of antiarrhythmic drugs is effective treatment for AF in patients with LV dysfunction.