Sudden cardiac death in young adults can be due to a range of conditions including coronary disease, hypertrophic or dilated cardiomyopathy, and arrhythmogenic right ventricular cardiomyopathy. Although each of these disorders has typical pathologic findings, some victims display no overt abnormalities and are presumed to have died from a primary cardiac arrhythmia. Increasingly, these malignant arrhythmias have been demonstrated to be due to mutations in ion channels. In this review we focus on the two most common of these disorders, termed ion channelopathies, namely congenital long QT syndrome and Brugada syndrome.