To assess the efficacy of dronedarone versus placebo for the maintenance of normal sinus rhythm after electrical, pharmacological or spontaneous conversion of atrial fibrillation/atrial flutter (AF/AFL).

To assess the efficacy of dronedarone versus placebo on AF/AFL-related symptoms.

To assess the efficacy of dronedarone versus placebo on ventricular rate control in case of AF/AFL recurrence.

This is a double-blind, parallel arm, placebo-controlled, multicentre, multinational, phase III study.

To be eligible, patients must be in normal sinus rhythm at randomisation and must have an ECG-documented history of recent AF/AFL reverted to normal sinus rhythm by electrical, pharmacological or spontaneous conversion

Inclusion Criteria:

• Patients of either sex aged 21 years or more, in sinus rhythm for at least 1 hour at the time of randomization and with at least one ECG-documented AF/AFL episode in the last 3 months.

Exclusion Criteria:

• MAIN CRITERIA (non-exhaustive list, see protocol for details):

Women of childbearing potential without adequate birth control, Pregnant women, Breastfeeding women, Congestive heart failure NYHA class III or IV, Conditions which increase the risk of severe antiarrhythmic drug side effects, Severe associated conditions.