Cardiac resynchronization therapy(CRT) is a new therapeutic option for patients who have drug-refractory end-stage heart failure. Much information has been obtained from patients who have sinus rhythm, but the use of CRT in patients who have chronic atrial fibrillation(AF) has not been studied extensively. Accordingly, we evaluated the clinical response and long-term survival rate of CRT in patients who had heart failure and chronic AF, and the results were compared with those in patients who had sinus rhythm and who underwent CRT. Sixty patients who had end-stage heart failure(30 had sinus rhythm and 30 had chronic AF), New York Heart Association classes III to IV, left ventricular ejection fraction< 35%, QRS interval >120 ms, and a left bundle branch block received a biventricular pacemaker. New York Heart Association class, Minnesota Quality of Life score, and 6-minutew-alking distance were evaluated at baseline and after 6 months of CRT. Longterm follow-up was ≤2 years. New York Heart Association class, Minnesota Quality of Life score, and 6-minute walking distance improved significantly in the 2 groups after 6 months of CRT. The number of nonresponders was greater among patients who had AF.Nevertheless, the long-term survival rate was comparable between patients who had sinus rhythm and those who had AF. Patients who had AF demonstrated comparable benefit from CRT as those who had sinus rhythm. Cardiac resynchronization therapy (CRT) is a new therapeutic option for patients who have drug-refractory end-stage heart failure. Much information has been obtained from patients who have sinus rhythm, but the use of CRT in patients who have chronic atrial fibrillation Has, has been studied extensively..,, we evaluated the clinical response and long-term survival rate of CRT in patients who had heart failure and chronic AF, and the results were compared with those in patients who had sinus rhythm and who underwent CRT. Sixty patients who had end-stage heart failure (30 had sinus rhythm and 30 had chronic AF), New York Heart Association classes III to IV, left ventricular ejection fraction <35%, QRS interval> 120 ms, and a left bundle branch block received a biventricular pacemaker. New York Heart Association class, Minnesota Quality of Life score, and 6-minutew-alking distance were evaluated at baseline and after 6 months of CRT. Longterm follow-up was ≤2 years. New York Heart Association class, Minnesota Quality of Life score, and 6-minute walking distance improved significantly in the 2 groups after 6 months of CRT. The number of nonresponders was greater among patients who had AF. Promising, the long-term survival rate was comparable between patients who had sinus rhythm and those who had AF. Patients who had AF demonstrated comparable benefit from CRT as those who who sinus rhythm.