KCNH2 and torsades de pointes: Based on the comparison of hERG or IKr activity, cardiac action potential duration, and QT prolongation against QT effects and reports of arrhythmogenic (torsade de pointes) potential of 100 drugs, a margin of 30-fold between hERG EC50 and Cmax was proposed to be an acceptable degree of safety regarding arrhythmogenesis (Redfern et al. 2003).