Conduction disorders result in cardiac arrhythmias that may be fatal. Histiocytoid cardiomyopathy, Arrhythmogenic right ventricular dysplasia, Isolated noncompaction of the left ventricle, Long QT syndrome (LQTS) and Brugada syndrome, are all well described. Congenital short QT syndrome is a new familial primary electrical disease of the heart, which is characterized by abnormally short QT interval and paroxysmal atrial and ventricular tachyarrhythmias, including sudden cardiac death. An autosomal dominant mode of inheritance has been suggested. Catecholaminergic polymorphic ventricular tachycardia is an inherited disease and occurs in the absence of structural heart disease or known associated syndromes. Although the histological appearance of some of these disorders may be diagnostic, molecular analysis is necessary to define clearly the particular type of cardiomyopathy.