Type of Participant and Disease Characteristics: - Clinical diagnosis of CPVT, based on documented history of polymorphic or bidirectional non-sustained ventricular tachycardia with exercise or ventricular ectopy in a pattern consistent with CPVT on EST. - Central Screening laboratory determination of a RYR2 variant that is pathogenic or likely pathogenic for CPVT. - Documented history of life-threatening ventricular arrhythmic event defined as: survived sudden cardiac arrest, sudden cardiac arrest with appropriate implantable cardioverter defibrillator (ICD) shock, arrhythmic syncope, or sustained ventricular tachycardia (30 seconds or more) with or without ICD shock. - On stable dose (defined as no change in dose by more than 50% for at least 1 month prior to Screening) of standard-of-care therapy defined as a beta-blocker and/or flecainide. - Documented prior history of EST demonstrating a ventricular arrythmia score (VAS) score of ≥ 2. - For the first 2 participants in each cohort only: a properly functioning ICD device in place. Following review of data from Cohorts 1 and 2, the Data Safety and Monitoring Board (DSMB) will determine if this criterion is required for participants in Cohort 3. - Must be up to date with meningococcal vaccination per national guidelines or willing to receive meningococcal vaccine to achieve this. - Other inclusion criteria to be applied as per protocol.

• Abnormal liver function: gamma-glutamyl transferase (GGT) > 1.5 × upper limit of normal [ULN] or total bilirubin > ULN). - Abnormal renal function defined by estimated glomerular filtration rate < 60 milliliter /minute (mL/min)/1.73-square meter (m^2) using Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) Formula. - Clinically significant abnormalities of coagulation including international normalized ratio or activated partial thromboplastin time > 1.2 × ULN or platelets < 150,000 cells/cubic millimeter (mm^3). - Potential concomitant cardiomyopathy or inherited arrhythmia as evidenced by pathogenic or likely pathogenic mutation other than RYR2 obtained on cardiac panel during Screening. - Current or prior treatment with an approved or investigational gene transfer drug. - Exposure to another investigational drug within 90 days prior to Screening or 5 half-lives since last administration, whichever is longer. - Contraindication or unwillingness to receive required immunosuppression regimen. - Body mass index ≥ 30 kilograms per square meter (kg/m^2). - Other exclusion criteria to be applied as per protocol.