BACKGROUND Left atrial volume and exercise capacity are strong predictors of cardiovascular risk. Decreased exercise capacity is expected when LAV is increased due to its association with abnormal left ventricular filling pressure. However, LAV enlargement is expected in chronic mitral regurgitation as well. OBJECTIVE To examine the link between LAV and exercise capacity in chronic MR and to determine whether larger LAV has indeed better exercise capacity in patients with chronic severe degenerative MR and good LV systolic function. METHODS The study included asymptomatic patients with severe chronic degenerative MR and normal LV systolic function that underwent stress echocardiography. LAV was measured at rest using the biplane Simpson's method and indexed to body surface area. The cutoff of good exercise capacity was determined at 7 METS. RESULTS The patient group comprised 52 consecutive patients (age 60 +/- 14 years, 36 males). Two subgroups (19 vs. 33 patients), age- and gender-matched, were formed according to LAVi cutoff of 42 ml/m2. Those with higher LAVi had lower exercise capacity (P = 0.004) albeit similar MR grade, baseline blood pressure, LV function and size. Receiver-operator curve analysis revealed indexed LAV value of < or = 42 as 51% sensitive and 88% specific for predicting exercise capacity > 7 METS (AUC = 0.7, P = 0.03). In multivariate analysis, age, gender and LAVi were identified as independent predictors of exercise capacity. CONCLUSIONS In asymptomatic patients with severe chronic degenerative MR and normal LV systolic function, mild enlargement of the left atrium (< or = 42 ml/m2) is associated with good exercise capacity.