KCNH2 gene mutations are (together with KCNQ1) one of the top two identified inherited causes of the cardiac arrhythmia Long QT Syndrome (LQTS), which results from delayed ventricular myocyte repolarization, manifests as a prolonged electrocardiogram QT interval (Figure 1B), and can cause lethal ventricular fibrillation (Curran et al., 1995; Sanguinetti et al., 1995). Here, KCNH2 is linked to familial long QT syndrome.