Safety and Efficacy of Vanoxerine for the Conversion of Subjects With Recent Onset Atrial Fibrillation or Flutter to Normal Sinus Rhythm

Inclusion Criteria: * Subject has been informed of the investigational nature of this study and has given written informed consent in accordance with institutional, local, and national guidelines. * Able to return for Day 8 follow up. * Male or female 18 years of age or greater. * Onset of AF/AFL within the 7 calendar days preceding randomization, based on symptoms. * AF/AFL documented by ECG during the screening period. * Adherence to local clinical standards or the ACC/AHA or ESC practice guidelines for AF/AFL regarding thromboembolic event prevention and treatment. Exclusion Criteria: * Previous exposure to vanoxerine HCl. * Women of childbearing potential (neither surgically sterilized nor post-menopausal defined as cessation of menses for over one year) * Systolic blood pressure \<110 mmHg (unless documented to be usual value). * Average heart rate \<60 bpm documented by screening ECG. * Average QTc \>440 msec documented by screening ECG. * QRS interval \>140 msec documented by screening ECG. * Paced atrial rhythm on screening ECG. * History of receiving another Class I or Class III antiarrhythmic drug within 3 days prior to randomization. Excluded Class I antiarrhythmic drugs include quinidine, procainamide, disopyramide, lignocaine, mexilitine, flecainide, and propafenone. Excluded Class III drugs include dofetilide, sotalol, dronedarone, and ranolazine. * History of amiodarone (oral or IV) within the 90 days prior to randomization. * Native or prosthetic aortic or mitral stenosis with aortic valve area ≤1.0 cm2 or mitral valve area of \<1.5 cm2 or any other valvular diseases for which surgery is indicated. * Treatment with any loop diuretic (e.g., furosemide, bumetanide, torsemide, ethacrynic acid, etc.) in the 30 days prior to randomization. * Ejection fraction of \<35% within the 3 months prior to randomization (most recent measure if more than one). * AF/AFL as a result of surgery (postoperative AF/AFL) within 30 days prior to randomization. * History of electrical cardioversion within the 7 calendar days prior to randomization. * History of any polymorphic ventricular tachycardia including torsades de pointes. * History or family history of long QT syndrome or other inherited arrhythmia syndrome. * History of ventricular tachycardia requiring drug or device therapy.