The availability of chromosomal markers that span the human genome and improved high-throughput technology for genotyping and sequencing have led to major advances against genetic diseases. Genes have been identified for several disorders responsible for arrhythmias and sudden death. These genes all encode ion channels and are referred to as channelopathy genes. Congenital long QT syndrome is caused by mutations in genes encoding sodium or potassium channels. Brugada syndrome, only recently described, is due to mutations in a sodium channel and is an important cause of sudden death, particularly in Southeast Asia. Familial polymorphic ventricular tachycardia is due to a defect in the ryanodine receptor. A locus mapped to 10q32 is responsible for familial atrial fibrillation. Treatments based on knowledge of the molecular defect are being implemented for long QT syndrome and will probably provide paradigms for targeted treatment of acquired arrhythmias.