Recent advances in molecular biology have had a major impact on our understanding of the mechanisms of human diseases. Electrophysiology is one of the areas which, besides others, has substantially benefited from this development. Our understanding of the structure, function and mechanisms of the regulation of ion channels as well as their contribution to the pathogenesis of cardiac arrhythmias has substantially increased. The results of these studies are not only of special interest from the scientific point of view. It is likely to assume that, in the future, they will increasingly influence the diagnosis and treatment of arrhythmias.