Study of K201 Injection on Restoration of Sinus Rhythm in Subjects Who Are in Atrial Fibrillation

Inclusion Criteria: * Symptomatic atrial fibrillation * Atrial fibrillation documented by ECG * Adherence to local clinical standards or the ACC/AHA/ESC practice guidelines for atrial fibrillation regarding thrombo-embolic event prevention and treatment. Exclusion Criteria: * Systolic blood pressure \<100 mmHg * Heart rate \<50 bpm * Temperature \>38°C * QT or QTcB \>440 ms * QRS \>140 ms * Paced atrial or ventricular rhythm on ECG * Serum potassium \<3.5 meq/L * History of receiving another intravenous Class I or Class III antiarrhythmic drug within 3 days of randomization * History of amiodarone in last 6 months. * Clinical evidence of acute coronary syndrome * Acute pulmonary edema or embolism * Hyperthyroidism * Acute pericarditis * History of failed electrical cardioversion at any time * History of torsades des pointes * History of familial long QT interval syndrome * History of ventricular tachycardia requiring drug or device therapy * History of NYHA Heart Failure Class 3 or 4.