Objective: Congestive heart failure(CHF) is associated with increased incidence of AF. The BNP level is a useful parameter for diagnosis of CHF. Measured from the signal-averaged P wave electrogram(P-SAECG), prolonged duration of signal averaged P wave has been associated with earlier recurrence of AF after cardioversion and a higher risk of development of AF. We evaluate the effect of elevated BNP to the parameter of P-wave signal averaged ECG in patients with CHF Design : The P-SAECG was assessed at 2nd day after admission, and the plasma level of BNP were measured in 61 consecutive patients with CHF without prior supraventricular arrhythmia and with non-CHF patients. Echocardiographic and clinical data were also recorded. We compare the parameter of P-SAECG, and other data in elevated BNP group and normal BNP group. Results : In all patients, there are high correlation between parameters of P-SAECG and BNP level. Elevated BNP level was associated with an increased root mean square (RMS) 40, 30 and 20 voltage. Compare two groups, there are significant difference in RMS 40, 30, 20 voltage and RMS p voltage. Conclusion : Increased RMS 40, 30, 20 voltage and p voltage were noted in patients with elevated BNP in CHF patients. In heart failure, preventive use of non-membrane active drug such as ACEI and ARB for AF substrate modification are important for prevention of future AF development.