Markers for pro-arrhythmia such as APD prolongation and triangulation were more pronouncedly induced by HERG/IKr-blocking drugs erythromycin and E-4031 in LQT1 than in LMC rabbits and the pro-arrhythmic marker increased spatial APD dispersion was induced by erythromycin only in LQT1 rabbits. The gene discussed is KCNH2; the disease is long QT syndrome 1.