The most common inherited forms of LQTS (>80% of sequenced cases) are caused by loss-of-function mutations in either of the main ventricular myocyte repolarizing voltage-gated potassium (Kv) channels, KCNQ1 (Kv7.1) and hERG (KCNH2; Kv11.1), while a further 10% of cases are caused by gain-of-function mutations in SCN5A, encoding the Nav1.5 voltage-gated sodium channel3. Here, SCN5A is linked to familial long QT syndrome.