Longer QT intervals have been shown to induce cardiovascular events, including atrioventricular (AV) block, ventricular tachycardia, and torsades de pointes in long QT syndrome (LQTS). We report the case of a male neonate with 2:1 AV block and congenital LQTS who died suddenly 45 days after birth. He was the first of dizygotic twins, born full-term, and weighed 2,516 g. His pulse was below 90 bpm, and electrocardiogram showed a 2:1 AV block and long QT interval (QTc 0.59). There was no history of sudden death in his family. In addition, no structural cardiac anomalies were detected on ultrasonography imaging. His pulse would rise to 120 bpm when he cried, and his QT interval tended to be shorter. He was discharged on day 7 and was kept under observation without medication. At day 45, he had syncope and was brought immediately to our hospital. He was in a state of cardiopulmonary arrest and died despite resuscitation. Although implantable cardioverter defibrillators have been successfully used in patients at high risk for LQTS, their use is controversial in asymptomatic patients or in those without a family history of sudden death. We report a case of neonatal LQTS and provide a review of the literature.