Abstract There are >500 pathologic variants within 17 genes causing congenital long QT syndrome, which leads to polymorphic ventricular tachycardia (pVT) and sudden cardiac death (SCD). About 30% of the mutations are concentrated in the KCNH2 gene resulting in loss-of-function of the rapidly activating delayed rectifier potassium current IKr causing prolongation of the action potential duration and QT interval (LQT2). We developed a transgenic rabbit model for LQT2 that recapitulate the human phenotype. This application is aimed at developing gene therapy for LQT2 using our rabbit model and an AAV9-mediated mosaic gene expression of hERG. Aim 1 to rescue the phenotype of LQT2G by delivering AAV9-encoded shRNA that will abolish expression of both the human pore mutant transgene and endogenous rERG with an shRNA-resistant hERG (hERG*) under the control of the CMV promoter at doses of 6E13vg/kg and 2E14vg/kg as compared to vehicle control. The Aim also proposes to study the cellular phenotype of the treated rabbits as compared to vehicle control. Aim 2 proposes to monitor ant test the two groups for spontaneous and inducible arrhythmias. This application outlines the roadmap for gene therapy of all variants causing human LQT2 syndrome and has the potential to revolutionize the therapy of this syndrome.