Abstract Introduction Patients with primary moderate or severe mitral regurgitation (MR) often remain asymptomatic for a long time due to mechanisms of compensation. Exercise stress could provoke symptoms, unmask subclinical changes of left and right ventricles and reveal decreased functional capacity. Reduced exercise capacity is related to worse outcomes. Purpose The aim of this study was to evaluate an exercise capacity and factors influencing it in patients with asymptomatic primary moderate to severe MR and preserved left ventricle (LV) ejection fraction (EF). Methods 60 patients with asymptomatic moderate or severe MR and LV EF >60% underwent resting and stress (bicycle–ergometry as per protocol 25 + 25W every 3 minutes) echocardiography. Their exercise capacity was evaluated in Watts (W) and metabolic units (MET). The blood sample for NT-proBNP evaluation was collected just before the stress test. Results Patients with primary MR achieved 84.74±35.16 W and 4.87±1.51 MET. According to univariate linear regression analysis exercise capacity in MET was significantly related to age (B=−0.066, p<0.001), systolic pulmonary artery pressure (SPAP) at rest (B=−0.048, p=0.034), resting E wave (B=−0.015, p=0.031) and NT-proBNP (B=−0.003, p=0.006). Predictors of exercise capacity in W also were age (B=−1.273, p=0.002), resting E wave (B=−0.318, p=0.041), NT-proBNP (B=−0.057, p=0.018). Higher concentration of NT-proBNP and bigger SPAP at rest correlated with lower exercise capacity (picture 1). In patients who had exercise induced pulmonary hypertension (EIPH; SPAP >60 mmHg during peak stress) ergometry was more frequently terminated prematurely (19 (95%) and 24 (60%), p=0.012). They also had significantly lower exercise capacity than subjects without EIPH ((W: p=0.015 and MET: p<0.001). Conclusions Age, NT-proBNP concentration, resting SPAP and E wave were predisposing factors of exercise capacity in patients with asymptomatic primary moderate to severe MR and preserved LV EF. EIPH and elevated NT-proBNP were related to premature exercise termination and lower exercise capacity. Funding Acknowledgement Type of funding sources: None. Picture 1