Background: Plasma B-type natriuretic peptide (BNP) is a useful diagnostic and prognostic biomarker for patients with congestive heart failure. In victims with cardiac arrest, plasma BNP level might reflect the presence of congestive heart failure prior to the occurrence of cardiac arrest. Influence of cardiac arrest on Plasma BNP level remains to be investigated. Purpose: The aim of this study is to know whether the occurrence of cardiac arrest influences on plasma BNP level and to define clinical significance of increased plasma BNP level in patients with cardiac arrest. Subject and methods: Seventy patients (mean age: 63짹16 year old, 49 males) with out-of-hospital cardiac arrest were enrolled in this study. Blood samples for BNP testing were obtained on arrival and at 30 minutes after initiation of CPR. Patients were grouped by plasma BNP level as normal BNP group (<100 pg/dl) and high BNP group (���100 pg/dl). Results: Plasma BNP was elevated (���100 pg/dl) in 37 patients and normal in 33 patients. Mean plasma BNP on arrival was 41짹29 pg/dl in normal BNP group and 876짹1049 pg/dl in high BNP group. Mean plasma BNP at 30 minutes after CPR initiation was 31짹32 pg/dl in normal BNP group and 585짹421 pg/dl in high BNP group. Mean plasma BNP of the patients with presumed cardiac etiology was higher than patients with non-cardiac etiology (709짹924 pg/dl vs 292짹777 pg/dl on arrival, p=0.44, 438짹463 vs 101짹180 pg/dl at 30 min., p=0.01) Plasma BNP was elevated in 24 (75%) of 32 patients with presumed cardiac etiology and 13 (34%) of 38 patients with non-cardiac etiology (p=0.01). There was no difference in plasma BNP level according to initial presenting cardiac rhythm or resuscitation outcome. Conclusion: Plasma BNP is not affected by occurrence of cardiac arrest or performing CPR. Elevated plasma BNP in patients with cardiac arrest suggests presence of preexisting heart disease.