 Atrial fibrillation AF is a common arrhythmia. The proposed patholophysiological mechanisms of AF include abnormal electrical conduction in atrium and sympathovagal imbalance with increased vagal tone. Patients with AF have poor exercise capacity that may contribute to decreased atrial effective refractory period, and decreased cardiac output and heart rate reserve, and may result in poor quality of life. Poor endothelial function had been noted in patients with AF, associated with increased risks of cerebrovascular and cardiovascular disease. Exercise training has been noted to improve exercise capacity and quality of life in patients with AF only in some studies. Endothelial function can be improved by exercise training in patients with cardiovascular disease, but no report in patients with AF. Evidence of exercise training is still needed in patients with AF. The purpose of this study is to investigate the effect of exercise training on 