In this proof of concept study, we have therefore investigated whether transgenic LQT1 rabbits with a reduced repolarization reserve may constitute a sensitive, novel tool for the detection of HERG/IKr-blocking properties of drugs, analyzing the impact of the antibiotic drug erythromycin and the class III anti-arrhythmic drug E-4031 on established markers of pro-arrhythmia, such as prolongation of APD, spatial APD dispersion and triangulation. Here, KCNH2 is linked to cardiac arrhythmia.