Introduction: To determine whether elevated N-terminal pro-BNP (NT pro-BNP) predicts pulmonary artery systolic pressure increase on exercise stress echocardiography in asymptomatic or mildly symptomatic patients with moderate to severe mitral stenosis. Methods and Results: Forty-one asymptomatic or mildly symptomatic patients with moderate to severe mitral stenosis and 21 age- and sex-matched healthy subjects. Transthoracic echocardiography was performed in all patients to assess the severity of the valve disease and to measure pulmonary artery pressure before and immediately after treadmill exercise. Blood samples for NT pro-BNP were also collected before and immediately after treadmill exercise at the time of echocardiographic examination. The plasma concentrations of NT pro-BNP levels were significantly higher in patients with mitral stenosis than in control subjects before and after exercise (P < 0.001). Patients with atrial fibrillation had significantly higher NT pro-BNP levels compared to those with sinus rhythm (P < 0.001). Pre- and postexercise NT pro-BNP levels correlated statistically significantly with the left atrial (LA) dimension, right ventricle enddiastolic diameter, exercise duration, heart rate, rest, and exercise pulmonary artery systolic pressure, after exercise mitral valve mean gradient. Area under the receiver-operating characteristic curve for NT pro-BNP as an exercise induced augmentation of pulmonary artery pressure was 0.78. Using an optimized cutoff value of 251 pg/mL for NT pro-BNP, sensitivity was 89.47%. The independent determinants of higher pulmonary artery pressure were LA diameter and pretest NT pro-BNP levels in multivariante analysis. Conclusion: NT pro-BNP levels correlate with functional class and echocardiographic findings in patients with mitral stenosis and indicate exercise induced augmentation of peak PAP > 60 mmHg. (Echocardiography 2011;28:8-14).