[Case report of TGA-1 neonate with hyponatremia].

A neonate with transposition of the great arteries (TGA) was scheduled for arterial switch operation (ASO) and entered to Pediatric ICU on day 4. Although mainly fed with mother's and formula milk, the serum natrium concentration decreased extremely to 104 mEq x l(-1) on day 9. We prioritized treatment of electrolyte disorders, and the operation was postponed on day 13. After the operation, he was diagnosed as syndrome of inappropriate secretion of antidiuretic hormone (SIADH) and post operative course was uneventful. Electrolyte control is very important even if the infant is fed with mother's milk.