In E-4031 treated LQT1 hearts, in contrast, a greater E-4031-induced APD prolongation than in LMC rabbits was seen only at low concentrations (0.003 μM and 0.01 μM) in the base-lateral segment, due to a higher susceptibility to E-4031's HERG/IKr-block in LQT1 rabbits, while higher concentrations of E-4031 resulted in a complete HERG/IKr-block in both, LQT1 and LMC rabbits, thus abolishing genotype differences. Here, KCNH2 is linked to long QT syndrome 1.