The investigators will propose a single-center, randomized, double-blind, phase II clinical trial in children undergoing Fontan surgery. The investigators plan to compare the effects of perioperative nesiritide, milrinone and placebo infusions on the early postoperative clinical course and neurohumoral profile. The investigators hypothesize that, when compared to the milrinone and placebo groups, the nesiritide group will have more days alive and out of the hospital within the first 30 days after surgery.