Evaluation the predictive value of perioperative Plasma B-type natriuretic peptide level in arterial switch operation. Plasma B-type natriuretic peptide level was measured before and and 24 hours after surgery in 29 patients with arterial switch operation. We evaluated 29 patients (22 male,76%,7 female 24%) with mean age 67.93±84.09 days (range 6 days to 14months).The mean of BNP level before surgery was 7989.96±9691.94 and increased after surgery to 22391.35±11898.67 and difference between two groups was significant (P=0.003).In linear regression test the BNP did not correlate with sex(r=0.33, P=0.085) and age(r=0.14,P=0.45). Furthermore, BNP did not correlate with duration of mechanical ventilation (r=0.132,P=0.53) , ICU stay (r=0.137,P=0.52) and with lactate level (r=0.41,P=0.054)after operation. During the study 4 patients(13.8%) died and the mean of BNP 24h after operation among them was 35000.00±00.00.using chai-square and fisher exact test the correlation between BNP and death was significant(P=0.001). We implied that BNP level increased 24 hours after arterial switch operation, moreover we denoted it correlated well with the death rate and an increase in B-type natriuretic peptide 24 hours after surgery predicts poor postoperative outcome. However it did not correlate with duration of mechanical ventilation ,ICU stay and lactate level in this patients.