Department of Clinical Genetics1, Cardiology3, Academic Medical Centre, University of Amsterdam, Netherlands.Prince Sultan Cardiac Centre2, Riyadh, Saudi Arabia.Cardiac ion channels are pore-forming protein complexes that permit well regulated inward and outward movement of ionic currents across the cell membranes, which are critical components of cardiac electrical and mechanical function.Dysregulation of cardiac ion channel functions lead to a variety of inherited cardiac arrhythmia syndromes.Long QT syndrome (LQTS) and Catecholaminergic Polymorphic Ventricular Tachycardia (CPVT) comprise a significant majority of the various cardiac arrhythmia syndromes.LQTS is an inherited cardiac arrhythmia disorder characterized by prolongation of the QT interval; patients are predisposed to ventricular tachyarrhythmias and fibrillation leading to recurrent syncope or sudden cardiac death.To date, 70% of patients with LQTS demonstrate a mutation in one of the presently known 12 genes.The most common subtypes of LQTS are LQTS1, LQTS2 and LQTS3, caused by mutations in the cardiac ion channel genes KCNQ1, KCNH2 and SCN5A, respectively.