Background: Patients with diastolic dysfunction have an abnormal rise in left ventricular (LV) filling pressures with exercise. Since NT-proBNP is an indicator of elevated intracardiac pressure, exertional change of NT-proBNP may reflect the response of diastolic function to exercise. Objectives: We sought to investigate whether exertional change of plasma NT-proBNP is augmented in patients with HCM and if yes it is associated with imapired diastolic functional response to exercise. Methods: After resting echocardiography, thirty-two patients (26 male, mean age 55짹11) with HCM and 32 age and sex-matched controls performed a symptom-limited graded supine bicycle exercise. Echo-Doppler parameters were measured at each exercise stage. Blood sample for determination of plasma concentration of NT-proBNP was drawn at rest and at peak or immediate after exercise. Results Exercise duration was comparable between the groups (606짹166 vs 670짹149 secs, p=0.11). NT-proBNP levels at rest (941짹877 vs 64짹108 pg/ml, p<0.0001) and at peak exercise (1015짹934 vs 70짹122 pg/ml, p<0.0001) of patients with HCM were higher than those of controls. Exertional change of NT-proBNP in HCM (74짹109 vs 6짹15 pg/ml, p=0.001) were significantly higher than in controls accompanying with blunted E��� (early diastolic mitral annular velocity) response to exercise (1.8짹1.3 vs 3.6짹3.2 cm/s from base to 25W, p=0.013; 2.4짹2.0 vs 4.2짹2.8 cm/s from base to 50W, p=0.006). Conclusion: Response in NT-proBNP to exercise was augmented in patients with HCM associated with blunted diastolic longitudinal functional response.