Although exercise intolerance is a major symptom of patients with atrial fibrillation (AF), the factors limiting these patients' exercise capacity remains uncertain. This study evaluated the correlation of clinical and echocardiographic parameters with exercise capacity of patients with AF. In all, 73 patients (61 men and 12 women; mean age 61 years) with chronic AF were included in this study. Those patients with primary valvular diseases were excluded. Standard 2-dimensional and Doppler echocardiography was performed, and we averaged 10 consecutive measurements of each variable. Patients then underwent a symptom-limited treadmill exercise testing. We also measured patients' plasma levels of B-type natriuretic peptide before exercise testing. Of all clinical and echocardiographic parameters we assessed, age (r = -0.45, P = .006), ratio of early mitral inflow velocity to mitral annular velocity (r = -0.35, P = .032), and baseline heart rate were independent predictors of exercise capacity on multivariate regression analysis. In conclusion, patient's age, averaged ratio of early mitral inflow velocity to mitral annular velocity, and baseline heart rate provided useful information on exercise intolerance for patients with AF. Ratio of early mitral inflow velocity to mitral annular velocity, a noninvasive tool for estimating left ventricular filling pressure, may especially have important value for predicting functional capacity in this population as it has in individuals with in sinus rhythm.