A Study Comparing Vernakalant Therapy to Amiodarone Therapy in Acute Management of Recent Onset Atrial Fibrillation (AF) (MK-6621-055)

Inclusion Criteria: * Symptomatic AF (duration of current episode is ≤7 days), which is hemodynamically stable, and participant has no other condition at the time of screening that may result in acute hospitalization * If female and of reproductive potential, the patient agrees to remain abstinent or use 2 acceptable methods of birth control from time of screening until 30-day follow-up. * Weigh at least 45 kg * Receiving adequate anticoagulant therapy Exclusion Criteria: * Hypersensitivity to the vernakalant or amiodarone or to citric acid, sodium chloride, sodium hydroxide, or iodine * Severe aortic stenosis * Systolic blood pressure \<100 mmHg * New York Heart Association (NYHA) Class III or IV heart failure * Severe bradycardia, sinus node dysfunction, or second and third degree heart block in the absence of a pacemaker * Use of IV rhythm control anti-arrhythmics (Class I and III) within 4 hours of study drug administration * Acute coronary syndrome (including myocardial infarction) within previous 30 days * History of thyroid dysfunction * Severe acute respiratory failure or cardiovascular collapse * Participating in another drug study or has received an investigational drug within 30 days prior to enrollment * Pregnant or breast-feeding, or expecting to conceive from time of screening until 30-day follow-up