Hearts of adult female transgenic LQT1 and wild type littermate control (LMC) rabbits were Langendorff-perfused with increasing concentrations of HERG/IKr-blockers E-4031 (0.001–0.1 μM, n = 9/7) or erythromycin (1–300 μM, n = 9/7) and APD, APD dispersion, and triangulation were analyzed. This evidence concerns the gene KCNH2 and long QT syndrome 1.