The hereditary long QT syndrome (LQT) is a disease characterized by lengthened ventricular repolarization, diagnosed by the presence of a prolongation of the QT interval on the electrocardiogram (ECG) (Fig. 9.1) and associated with sudden cardiac death (SCD). The prevalence of the disease is thought to be around 1/5,000 of the general population. While the majority of patients with the LQT syndrome are at present asymptomatic, mainly due to the identification of family members during familial screening, the phenotype is varied and can range from asymptomatic individuals to syncopal episodes, seizures, malignant ventricular arrhythmias, and ventricular fibrillation. Approximately 1/3 of individuals present with syncope or aborted malignant ventricular arrhythmias, including torsades de pointes, which is the most typical ventricular arrhythmia in LQT syndrome. Symptoms in the LQT syndrome are limited to the cardiac system with the exception of individuals with the recessive form or Jervell and Lange-Nielsen who also present with neural deafness.1-6