OBJECTIVE: To describe our experience with low-dose arginine vasopressin infusions (0.0003 U/kg/min) initiated in the operating room after the Norwood procedure or arterial switch operation. DESIGN: Retrospective cohort study of 37 consecutive neonates. SETTING: Pediatric cardiovascular intensive care unit in a tertiary hospital. SUBJECTS: Nineteen patients that received low-dose arginine vasopressin infusion instituted in the operating room (arginine vasopressin+) were compared to 18 patients that did not receive early arginine vasopressin infusion (arginine vasopressin-). INTERVENTIONS: None. RESULTS: When comparing arginine vasopressin+ and arginine vasopressin- in the first 24 hrs after cardiovascular intensive care unit admission, there was no difference in demographic variables, heart rate, blood pressure, central venous pressure, maximum lactate, maximum arterial and central venous saturation difference, urine output, chest tube output, or peritoneal drain output. Mean fluid resuscitation in the first 24 hrs was significantly lower in the arginine vasopressin+ group compared to the arginine vasopressin- group (182 ± 61 mL/kg vs. 223 ± 53 mL/kg, p = .03). The arginine vasopressin+ group also reached median net negative cumulative fluid balance sooner (55 hrs: interquartile range 45, 74 vs. 76 hrs: interquartile range 69, 92; p = .02). Median maximum inotrope score in the first 24 hrs was significantly lower in arginine vasopressin+ (9: interquartile range 5, 12.5 vs. 16.5: interquartile range 10.3, 22.1; p = .02). There was a nonsignificant trend toward shorter duration of mechanical ventilation and cardiovascular intensive care unit length of stay in the arginine vasopressin+ group. The lowest serum sodium in the first 48 hrs was significantly lower in arginine vasopressin+ (132 vs. 137 mmol/L, p = .01). CONCLUSION: Low-dose arginine vasopressin infusion initiated in the operating room after complex neonatal cardiac surgery was associated with decreased fluid resuscitation and catecholamine requirements in the first 24 postoperative hours. Copyright © 2012 by the Society of Critical Care Medicine and the World Federation of Pediatric Intensive and Critical Care Societies.