Background: A robust association between BNP and NT-proBNP and the short- and long-term risk of death of acute coronary syndrome has recently been demonstrated. NT-proBNP concentrations are considerably higher in most patients, probably due to decreased clearance as BNP and NT-ProBNP initially are produced in equimolar quantities. We don���t know which one is better to measure BNP or NT-proBNP in ACS. Method: To determine which one is associated with LV dysfunction and myocardial ischemia, we mreasured plasma BNP or NT-proBNP at admission in 32 unstable angina and 49 non-ST elevated MI patients who visited emergency room within 24 hours after onset of chest pain. LV ejection fraction(LVEF) and myocardial ischemia/infarction area were measured with gated Tc-99m MIBI myocardial perfusion scan. Results; NT-proBNP was correlated with LVEF (r=0.663, P=0.001), ischemic risk area (r=0.663, P=0.003) and infarction area (r=0.516, P=0.028). BNP also correlated with LVEF (r=-0.323, p=0.045), ischemic risk area (r=0.355, P=0.042) and infarction area (r=0.405, P=0.019). Furthermore BNP was correlated with troponin-T measured at admission (r=0.443, P=0.005) unlike NT-proBNP. Conclusions: Elevated NT-proBNP is more correlated with the size of myocardial ischemia/infarction area than BNP in ACS patients.