The primary objective of this study is to:

Assess whether the addition of dronedarone to existing conventional rate control therapy leads to a reduced ventricular rate after 1 week in patients with a high Heart Rate (HR) at rest during Atrial Fibrillation (AF) in comparison to an increase of conventional therapy.

The secondary objectives of this study are to compare both study arms with regard to:

• Ventricular rate after 3 months
• Number of registered AF episodes
• Number of symptomatic AF episodes
• Severity of AF and AF-like symptoms
• Rate of premature study discontinuation
• Number of symptomatic episodes of bradycardia
• Incidence of low heart rate (<60 bpm)

Inclusion Criteria:

• Persistent AF with HR >80 bpm at rest despite treatment with ≤ 2 rate control agents (i.e. beta blocker and/or calcium antagonist - Patients using digoxin are eligible)
• Documented AF in the past 24 hours
• Treated with the following rate control medication:
• beta blocker or
• calcium antagonist or
• beta blocker plus calcium antagonist or
• beta blocker plus digoxin or
• calcium antagonist plus digoxin
• Anticoagulant treatment in line with local guidelines

Exclusion Criteria:

• Incapacitated patients
• Paroxysmal or permanent AF
• Use of class I or III anti-arrhythmic drugs in the past 12 weeks
• Scheduled cardioversion or pulmonary vein ablation
• Unstable New York Heart Association (NYHA) class III and all class IV Heart Failure
• AV block grade 2 or 3
• Known severe renal impairment (serum creatinine > 180 μmol/l)
• Known severe hepatic impairment (AST, ALT > 3 x Upper Limit of Normal (ULN))
• Contra-indication for dronedarone
• Participation in a clinical drug study in the 3 months prior to inclusion
• Women of childbearing potential, who do not use adequate contraception
• Lactating women

The above information is not intended to contain all considerations relevant to a patient's potential participation in a clinical trial.