Atrial fibrillation (an abnormal rhythm in the upper chamber of the heart) is a common supraventricular arrhythmia (a type of abnormal heart rhythm) for which antiarrhythmic therapy is often prescribed. The primary goals of therapy are to maintain sinus rhythm (normal heart rhythm) and to reduce the occurrence of episodes of atrial fibrillation. Azimilide may have an effect on increasing the time to first recurrence of symptomatic atrial fibrillation or atrial flutter and symptomatic paroxysmal supraventricular tachycardia (other types of abnormal heart rhythms).

This double-blind, placebo-controlled study is designed to evaluate the efficacy and safety of azimilide compared with placebo in prolonging the time to the first symptomatic arrhythmia recurrence in patients with a history of atrial fibrillation and congestive heart failure and/or ischemic heart disease) and those without these conditions. Once this phase of the study is completed, a second phase with a different study design will be conducted. The second phase is an open-label, follow-up phase. The follow-up phase of the study is designed to evaluate the long-term efficacy and safety of a daily oral dose of azimilide in patients who complete the double-blind, placebo-controlled phase of this study.

Inclusion criteria:

• History of symptomatic atrial fibrillation that significantly disrupts the patient's customary daily living activities
• History of congestive heart failure and/or ischemic heart disease
• Sinus rhythm (normal heart rhythm) upon entry to the 30 day screening period for the study
• At least one episode of symptomatic atrial fibrillation during the screening period, with a spontaneous return to sinus rhythm.
• Sinus rhythm immediately prior to dosing

Exclusion criteria:

• Previously unsuccessful cardioversions within 60 days of screening period
• Failed to respond to any Class III antiarrhythmic drugs
• Qualifying arrhythmia due to acute reversible illness, acute myocardial infarction, and/or cardiac or thoracic surgery within one month prior to randomization
• Previously in an azimilide study