Molecular biology is transforming the field of sudden cardiac death. Long QT syndrome (LQTS) is the first inherited channelopathy to boast largely complete genetic analysis. Since at least eight different genes are known to be involved, all but one encoding for sodium or potassium channel subunits, LQTS is no longer viewed as a single entity, but as a group of diseases sharing the feature of prolonged repolarization while differing in severity, prognosis, and management. Mutations exist in 60% of patients, while 30% of carriers have a normal QT interval, but an increased risk of arrhythmia on exposure to hypokalemia. The entry of genetics into clinical cardiology offers unparalleled diagnostic precision, but also the potential for novel risk stratification strategies and gene-specific prophylaxis against life-threatening arrhythmias...