Double blind study to evaluate the efficacy and tolerability of SSR149744C and select a dose to be further investigated in the maintenance of sinus rhythm after electrical, pharmacological or spontaneous conversion of AF/AFL.

This is a dose-ranging multicenter, multinational, randomized, double-blind, placebo-controlled, parallel arm study with 4 SSR149744C dose regimens and amiodarone as a calibrator.To be eligible, patients must be in normal sinus rhythm for at least one hour at randomization and must have an electrocardiogram documented history of recent AF/AFL reverted to normal sinus rhythm by electrical, pharmacological or spontaneous conversion.

Inclusion Criteria:

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

Exclusion Criteria:

• MAIN CRITERIA (non-exhaustive list):Women of childbearing potential without adequate birthcontrol, Pregnant Women, Breastfeeding women, contraindications to amiodarone, conditions which increase the risk of severe antiarrhythmic drug side effects, severe left ventricular dysfunction, severe associated conditions.