PRECISION-AF is designed as a single, adequate and well-controlled Phase 3 clinical trial that may be sufficient to support a New Drug Application (NDA) submission for an AF indication if the objectives of the trial are achieved. The trial is designed as a double-blind, active-controlled, multi-center, international study comparing Gencaro with Toprol-XL (metoprolol succinate) for the prevention of AF recurrence or all-cause mortality (ACM) in heart failure (HF) patients with left ventricular ejection fraction (LVEF) ≥ 40% and ≤ 55%. Patients with LVEF ≥ 40% and ≤ 55% constituted approximately half of the enrolled population in the Phase 2 GENETIC-AF trial. PRECISION-AF will enroll approximately 400 HF patients who have a LVEF ≥ 40% and ≤ 55%, a recent AF event, and the genotype which responds most favorably to Gencaro. The primary endpoint of the trial will be time to first event of atrial fibrillation/atrial flutter (AF/AFL) or ACM during the 26-week Follow-up Period. In the recently completed GENETIC-AF trial, Gencaro showed a 58% treatment benefit compared to Toprol-XL in reducing AF recurrence in the HF population targeted for Phase 3 (hazard ratio = 0.42; 95% CI: 0.21, 0.86; p = 0.017). With 400 patients (200 per arm) the trial will have 90% power at a p-value of 0.01 to detect a 45% treatment benefit for Gencaro compared to Toprol-XL.