In Phase 2, a total of 300 patients (3:2 randomization) will be enrolled in the study at up to 15 investigational sites in USA and Europe. Patients with AF who require electrical cardioversion will be enrolled into the study. The study will last for 8 weeks for each subject, with an estimated overall duration of 12 months (8 months enrollment period, 2 months follow-up period, remaining time for close-out) for the study.