In postmarketing surveillance, the main cause of cardiotoxicity such as long QT syndrome (LQTS), ventricular fibrillation, ventricular arrhythmia, and sudden death is inhibition of the human ether‐α‐go‐go‐related gene (hERG), which encodes the voltage‐gated potassium channel (Kv11.1) (Creanza et al. 2021). Here, KCNH2 is linked to familial long QT syndrome.