Purpose: N-Terminal Pro-Brain Natriuretic Peptide (NT-proBNP) has been introduced recently as a useful parameter for assessing left ventricular (LV) systolic function. But there were not so many reports about its usefulness in LV diastolic function. So we assessed the hypothesis that NT-proBNP correlates with diastolic functional parameters in the patients with normal ejection fraction (EF). Methods: From Febrary 2004 to April 2005, NT-proBNP was measured in 4,256 patients who complained dyspnea or chest pain in emergency room and out patient clinic. And we performed echocardiography measuring various LV systolic and diastolic parameters within a day. Among them, patients with atrial fibrillation, more than 1.8 mg/dl of serum creatinine and inadequate echocardiographic data were excluded. Fianally, 434 patients were enrolled and analyzed. Data are expressed as means 짹 standard error of mean or median (25th percentile-75th percentile). Results: Among paticipants (57.4% male, mean age 62.0짹0.7 years), 146 patients (33.6%) showed decreased LV systolic functions (EF<55%) and 134 patients (30.9%) revealed to acute coronary syndrome. NT-proBNP levels ranged from 5 to 35,000 ng/L with a median of 354.2 ng/L (interquatile range, 86.4 to 2265.0 ng/L). NT-proBNP showed significant correlations with EF by volumetry, LV mass index, left atrial volume index, right ventricular systolic pressure (RVsP), transmitral E /mitral annular E' (E/E') ratio and age (r=-0.548 and p=0.000, r=0.481 and p=0.000, r=0.440 and p=0.000, r=0.405 and p=0.000, r=0.368 and p=0.000 and r=0.340 and p=0.000, respectively). Interestingly, among 288 patients (56.6% male, mean age 60.4짹0.8 years) with normal EF (67.1짹0.5%), NT-proBNP showed significant correlations with left atrial volume index, RVsP, age, LV mass index, E/E��� ratio and LVEF by volumetry (r=0.406 and p=0.000, r=0.376 and p=0.000, r=0.309 and p=0.000, r=0.271 and p=0.000, r=0.256 and p=0.001 and r=-0.251 and p=0.017, respectively). Conclusions: NT-proBNP is a useful parameter for assessing LV diastolic function as well as systolic one in overall range of EF. Furthermore NT-proBNP reflects diastolic function better than systolic one in patients with normal EF.