In utero, the ductus venosus connects the left portal vein to the inferior vena cava, allowing a portion of the venous blood to bypass the liver and return to the heart. After birth, the ductus venosus closes due to changes in intracardiac pressures and a decrease in endogenous prostaglandins. Failure of the ductus venosus to close may result in galactosemia, hypoxemia, encephalopathy with hyperammonia, and hepatic dysfunction. We report an infant with complex congenital heart disease (CHD) who developed coagulopathy and hyperammonia during the preoperative period secondary to patent ductus venosus (PDV). Previous reports of PDV in CHD are presented, its etiology and clinical consequences reviewed, and options for therapeutic treatment discussed.