KCNH2 and cardiac rhythm disease: In particular, hERG channel, the molecular basis of the rapidly activating K+ current (IKr), is implicated in many life-threatening cardiac arrhythmias [13]–[18], and guidelines (ICH S7B) from regulatory agencies in the USA, European Union and Japan require that any new drug under development be tested for effects on the hERG current prior to first administration in humans [19].