A Study of IV HBI-3000 for the Conversion Recent Onset Atrial Fibrillation (AF)

Inclusion Criteria:

• 18 to 80 years of age

• Sustained AF of > 2 hours and < 72 hours duration

• Eligible for cardioversion (electrical and pharmacologic)

• On adequate anticoagulant therapy or eligible for anticoagulation during treatmentand for at least 30 days duration after treatment if indicated by ACC/AHA/HRS orcountry specific national or international guidelines for thromboembolic riskreduction related to AF

Exclusion Criteria:

• Atrial fibrillation < 2 hours or > 72 hours duration or with duration not reliablyestablished at the time of dosing

• Hemodynamic instability that may require emergency electrical cardioversion

• Atrial flutter

• Moderate to severe HF

• Clinical or ECG signs of acute cardiac ischemia or digitalis toxicity

• Known or suspected hyperthyroidism

• Cardiac surgery, stroke, TIA, acute MI/ PCI, unstable angina, or persistent anginaat rest within the previous 3 months

• Presence of LA thrombus by TEE or TTE

• Presence of concurrent myocarditis or endocarditis

• ECG abnormalities: Current QTcF > 480 msec; QRS interval > 120 msec and/or acomplete bundle branch block (BBB)l Delta wave or other pre-excitation patternconsistent with WPW syndrome; Acute coronary ischemia patterns

• Use of medication that prolongs the QTc interval or history of: Long QT syndrome,congenital or acquired; Torsades de Pointes (TdP); Brugada Syndrome; Ventriculararrhythmia (not including infrequent isolated PVC)

• Concurrent treatment with Class I or III antiarrhythmic drugs, metformin or strongCYP2D6 inhibitors (unless the medication is discontinued > 5 half-lives beforeenrollment)

• Treatment with oral amiodarone in the previous 3 months or IV amiodaroneadministered within 24 hours prior to planned Study Drug administration

• Use of vernakalant, or any experimental drug within 30 days or five half-lives (whichever is longer) of Study Drug administration, or use of an invasiveinvestigational medical device within 2 months prior to Study Drug administration,or current enrollment in another study with investigational agent or procedure

• Clinically significant laboratory abnormalities