Background and Objectives: While a relationship between the amio-terminal probrain natriuretic peptide (NT-proBNP) and impaired left ventricular function with or without heart failure after transmural infarction is reasonably anticipated, the findings of studies evaluating BNP in patients without or with minimal myocardial necrosis such as Non-ST elevation myocardial infarction (NSTEMI) have been intriguing. We studied whether the elevated NT-proBNP is correlated with the extent of left ventricular (LV) systolic dysfunction after NSTEMI and evaluated the NT-proBNP level as a marker of diastolic LV myocardial dysfunction in the patients with preserved LV systolic function after NSTEMI. Methods: Of the 202 patients with Acute Coronary Syndromes enrolled in the AMI registry of our hospital, 91 NSTEMI patients were recruited. We analyzed the linear regression between the initial demographic data, cardiac markers, and NT-proBNP (Roche, Elecsys), and cardiac functions with echocardiographic parameters. LV ejection fraction (LVEF), peak early velocity (E) by using mitral pulsed wave Doppler, mitral annular peak early velocity (E') of tissue Doppler imaging and E/E' ratio were used. Results: The age, peak troponin T, hsCRP, NT-proBNP, wall motion score (WMS) correlated with LV systolic ejection fraction (LVEF) and the NT-proBNP had a strongest correlation (p<0.001). The NT-proBNP showed still a strong correlation with E/E' ratio (9.0짹3.2) even in the patients (N=57) with preserved LV systolic function (EF>50%), but other factors did not. The NT-proBNP was the only marker of minimal myocardial necrosis and myocardial dysfunction in the patients with NSTEMI and preserved systolic function. Conclusions: The circulating NT-proBNP levels might be associated with the extent of myocardial ischemia and correlated with systolic and diastolic dysfunction in the patients with NSTEMI. These findings suggested the elevated NT-proBNP might be a marker of LV dysfunction in non-transmural myocardial infarction, and a very sensitive marker for diastolic dysfunction even in preserved systolic function.