Background: N-terminal pro-B type natriuretic peptide (NT-proBNP) has been introduced as a useful parameter for assessing left ventricular (LV) systolic function. However, correlations between NT-proBNP with diastolic echocardiographic parameters were not analyzed precisely. So, we sought to evaluate the clinical implication of NT-proBNP on the LV diastolic function in large scale databases of both. Methods: NT-proBNP database (n=23,029) and echocardiography database (n=48,750) were collected in a single center from April 2003 to January 2008. Cases which both were measured within 24 hours were enrolled and cases with more than 2.0 pg/ml of serum creatinine or acute coronary syndrome were excluded. Finally, echocardiographic parameters were compared with serum NT-proBNP levels in 1,852 patients combining clinical data. Results: Among patients (54% female, mean age 63.0짹0.3 years), 460 patients (24.8%) showed preserved LV systolic functions (ejection fraction (EF)���40%, 53.5짹0.4%). NT-proBNP levels ranged from 5 to 35,000 ng/L with a mean of 2319.7 ng/L. As we expected, NT-proBNP levels were significantly correlated with EF by volumetry (r=-0.52, p=0.01), left atrial volume index (r=0.50, p=0.01), transmitral E /mitral annular E���(E/E���) (r=0.44, p=0.01), right ventricular systolic pressure (r=0.43, p=0.01) and LV mass index (r=0.40, p=0.01). However, NT-proBNP showed low sensitivities to determine high E/E��� ratio above 15 and high LAVI above 27 on cut-off values of the ROC curve with the specificity of 80% (52.0% at 684.0 ng/L, 58.7% at 643.1 ng/L, respecitively). Interestingly, in patients with the preserved systolic function (55.9% male, mean age 61.2짹0.7 years), NT-proBNP showed slightly more sensitivities than the total study group (53.5% at 717.0 ng/L, 60.9% at 443.3 ng/L, respecitively). Conclusions: Although NT-proBNP was proved as a useful parameter for assessing LV diastolic function as well as systolic function in large scale database, it showed relatively low sensitivity to determining LV diastolic function. Therefore, NT-proBNP may imply LV diastolic function but should be interpreted with combining clinical information.