In the case of myocardial hypertrophy and heart failure (HF) the prolongation of action potential duration (APD) may consequently form early afterdepolarizations (EADs) (Nabauer and Kaab, 1998) Heart failure can cause a significant decrease in the repolarising Ito and delayed rectifier potassium currents (IKr and IKs currents of K channels encoded by KCNH2 and KCNQ1 genes) that may enhance the effect of proarrhythmic factors (e.g., hypokalemia, hypomagnesemia, class III antiarrhythmic drugs) (Nuss et al., 1996; Anumonwo and Lopatin, 2010). The gene discussed is KCNH2; the disease is heart failure.