[Background] Brain Natriuretic Peptide(BNP) is released from the cardiac ventricles in response to increased wall tension, resulting natriuresis and vasodilataion. Therefore, BNP is increased in congestive heart failure and acute myocardial infarction(AMI), and much of its relations to left ventricle has been reported. However, study of its relations with right ventricle is still insufficient. This study sought to investigate the usefulness of BNP in Right Ventricular Infarction(RVI). [Method] The patients those who were diagnosed with inferior AMI and performed primary coronary intervention were selected for this study. The subject patients(n=54) had a significant luminal narrowing(���70%) at right coronary artery, and no specific findings in left coronary artery on a coronary angiogram to rule out an increase of BNP by left ventricular dysfunction or infarction. A lesion was classified as a proximal lesion when it existed on the proximal portion of a right ventricular branch and as a distal lesion when it existed on the more distal portion than this. The patients were divided into group A for those who had a proximal lesion and RVI, group B also with a proximal lesion but no RVI, and group C with a distal lesion. [Result] 1) Seventeen(31%) of the 54 subject patients suffered from RVI, and all of them had stenosis in their proximal right coronary arteries. Among 37 patients who did not accompany with RVI, 16(43%) had a significant stenosis in their proximal portion while 21(57%) had a significant distal stenosis. 2) The level of BNP was 333.8짹238.5 pg/ml in group A(n=17), 83.2짹53.6 pg/ml in group B(n=16), and 68.1짹46.9 pg/ml in group C(n=21) respectively. BNP was increased when RVI was accompanied regardless of the site of a lesion (p<0.001). 3) There was no significant difference in the values of troponin I, CK-MB, and myoglobin, and the frequency of DM, HT, and hypercholesterolemia in each group. [Conclusion] For many of the patients who are diagnosed with inferior AMI and have a normal left coronary artery, an increased level of BNP is involved in RVI and related to poorer prognosis compared with in the case of a simple inferior AMI. Therefore, we suggest BNP as a useful tool for detection of RVI.