Background-Based on the close association of left atrial(LA) compliance with pulmonary hypertension in patients with mitral stenosis(MS), we hypothesized that 1)Doppler-derived net atrioventricular compliance(Cn) can be used for predicting the occurrence of mitral valve(MV) replacement or percutaneous mitral commissurotomy(PMC), and 2)determinants of exercise capacity are variable depending on Cn. Methods-We consecutively enrolled 26 patients(22 women;47.0짹6.1yrs) with pure moderate or severe MS, in whom comprehensive EchoCG was performed at rest. Cn was derived from the equation that has been previously validated(Cn = 1270 x (MV area by 2D planimetry / mitral E-wave downslope)). Measurements of stroke volume(SV) and systolic pulmonary artery pressure(sPAP) were repeated immediately after symptom-limited treadmill exercise test within 60 seconds. Results-Cn<4ml/mmHg was selected to define abnormally small Cn. Over a mean duration of 24-month follow-up, Cn<4 mL/mmHg could reliably predict the occurrence of either MV replacement or PMC, which was confirmed by multivariate analysis. In patients with Cn<4mL/mmHg, exercise duration was closely correlated with resting sPAP(r=-0.73,P=0.03), whereas in patients with Cn���4mL/mmHg, post-exercise SV was the only determinant of exercise capacity(r=0.49,P=0.04). Conclusions-In moderate or severe MS, LA compliance estimated by Cn with Doppler EchoCG allows us to effectively predict the event of MV replacement or PMC. In addition, determinants of exercise capacity were variable depending on the degree of Cn.