Long QT syndrome is a well-described entity in infants. Its presentation in the context of congenital heart disease is rare and is almost exclusively diagnosed postoperatively. For patients undergoing surgical intervention, preoperative knowledge of the diagnosis and appropriate perioperative management can be life-saving. We present the rare case of an infant with tetralogy of Fallot who was preoperatively diagnosed with long QT syndrome and discuss the implications of this diagnosis for his perioperative management.