Effects of Intravenous K201 on the Restoration of Sinus Rhythm in Subjects With Symptomatic Atrial Fibrillation

Inclusion Criteria: * Symptomatic atrial fibrillation for more than 3 hours and less than 7 days (as dated by symptoms). * Atrial fibrillation documented by ECG at the start of study drug infusion. Exclusion Criteria: * Previous exposure to K201 * QTcF (Fridericia correction) \>440 ms * QRS interval \> 140 ms * Paced atrial or paced ventricular rhythm on ECG * History of receiving another intravenous Class I or Class III antiarrhythmic drug within 3 days of randomization * History of amiodarone (oral or IV) in the last 3 months. * Clinical evidence or history of acute coronary syndrome (e.g. myocardial infarction, unstable angina) within 30 days prior to randomization * History of failed electrical cardioversion at any time in the past * History of polymorphic ventricular tachycardia (e.g. torsades des pointes) * History or family history of Long QT Syndrome * History of ventricular tachycardia requiring drug or device therapy * Ejection fraction of 40% or less.