Publisher Summary This chapter discusses the clinical features and management of arrhythmia disorders, and conduction disease. The current understanding of genetic and genomic abnormalities associated with these disorders is reviewed. Arrhythmias are thought to occur due to primary or secondary abnormalities in cardiac electrophysiology. These abnormalities include primary alterations in myocardial conduction and repolarization, or those occurring as a result of structural heart disease. A significant portion of the individuals found to have abnormalities of rhythm and conduction are now known to have a genetic basis, with familial inheritance notable. Familial inheritance of arrhythmias and conduction disorders indicates that genetic factors play an integral role in the development of these abnormalities. Understanding the underlying genetic defects provides an insight into the mechanisms leading to the clinical picture and promises to impact the therapeutic strategies used in the care of these patients. The entire cardiac electrical system is affected by genetic abnormalities, leading to atrial and ventricular tachyarrhythmias, sinus node dysfunction, or atrioventricular block. The long QT syndromes are primary disorders of cardiac repolarization in which prolongation of the QT interval corrected for heart rate is seen on the surface electrocardiogram along with abnormalities of T-wave morphology and sinus bradycardia.