The prolonged QT interval syndromes consist of two forms, one congenital and one acquired. The congenital form is probably due to an imbalance in the sympathetic nervous system supply to the heart. It is a preventable cause of sudden death both at an early age and during anesthesia. Recognition of congenital forms of prolonged QT interval and treatment with beta-adrenergic blockers have reduced the mortality. Special care in the perioperative period is necessary to prevent anesthetic-related deaths. The acquired form has many causes. These may be present preoperatively or they may occur intraoperatively. It is important that patients with ALQTS are recognized early and the underlying cause treated.