Genetically Targeted Therapy for the Prevention of Symptomatic Atrial Fibrillation in Patients With Heart Failure

Key Inclusion Criteria: * Must weigh at least 40 kg * Possess the β1389 Arg/Arg genotype * Left Ventricular Ejection Fraction (LVEF) \< 0.50 assessed within 12 months prior to Screening * At least one episode of symptomatic paroxysmal or persistent AF within 180 days of Screening * Clinically appropriate for electrical cardioversion (ECV) if AF/AFL is present after study drug initiation * Receiving appropriate anticoagulation therapy prior to Randomization Key Exclusion Criteria: * NYHA Class IV symptoms at the time of Randomization * Significant fluid overload at Randomization * Permanent AF at Screening * More than two previous ECV within 6 months of Randomization or if the most recent ECV failed to produce SR * Presence of an LVAD, or likely to requirement LVAD placement within 6 months of Randomization * History of a successful atrioventricular (AV) node ablation * History of an AF/AFL ablation within 30 days of Randomization * Evidence of an appropriate firing of an implanted cardioverter-defibrillator (ICD) device for ventricular tachycardia (VT) or ventricular fibrillation (VF) within 90 days of Randomization