Sudden death is often the first manifestation in inherited cardiac arrhythmia syndromes. Patients with long QT syndrome who have an episode of syncope while on beta-blockade should be offered an implantable cardioverter-defibrillator (ICD). In Brugada syndrome and hypertrophic cardiomyopathy, ICDs are often the most effective treatment of primary and secondary prevention of cardiac arrest. Risk stratification is crucial in identifying those at greatest risk to provide lifesaving therapy with an ICD while avoiding complications in those unlikely to receive benefit.