The general objective of this study is to demonstrate the effectiveness of n-3 fatty acids, 2.4 grams per day, to prevent recurrence of atrial fibrillation in patients with paroxysmal or persistent AF in whom a rhythm-control strategy is planned.

Atrial fibrillation (AF) represents the most common arrhythmia of clinical importance. The prevalence of AF in the general population has been estimated to be just below 1%, or 300,000 Canadians, and rising. Current strategies in AF to preserve normal sinus rhythm include pharmacological therapy with agents that demonstrate intermediate efficacy and significant adverse effects. Newer non-pharmacological strategies such as pulmonary vein ablation are suitable for only a minority of patients and are an expensive method of treatment. As a result, simple, safe, inexpensive and effective strategies to treat AF and preserve sinus rhythm are required given the great health and financial burden that this condition represents to our society.

Omega-3 or "n-3" polyunsaturated fatty acids (n-3 fatty acids) represent a novel approach to the prevention and treatment of AF. N-3 fatty acids have known anti-arrhythmic properties and are associated with a lower risk of sudden (arrhythmic) death. Additionally, n-3 fatty acids have significant anti-inflammatory properties and potential anti-oxidant effects. Higher consumption of non-fried fish was recently shown to confer a lower incidence of new onset AF in elderly adults. N-3 fatty acids might therefore represent a useful strategy for maintenance of sinus rhythm in patients with AF, given their potential to act on several mechanisms simultaneously. We seek to test this hypothesis in the current clinical trial proposal.

Inclusion Criteria:

1. Age > 18 years
2. Written informed consent
3. Non-valvular paroxysmal or persistent AF in whom a rhythm control strategy is planned
4. Duration of at least one symptomatic AF episode > 10 minutes within the past 6 months
5. ECG documentation of AF

Exclusion Criteria:

1. Chronic AF (continuously present for > 3 months)
2. Myocardial infarction within the past month prior to selection visit
3. Cardiac or thoracic surgery within the past 3 months or likely to be performed during trial
4. Moderate to severe congestive heart failure (NHYA FC III-IV)
5. Known left ventricular dysfunction (EF< 40%).
6. Mitral stenosis
7. Moderate to severe mitral insufficiency (Grade 3-4/4)
8. AF secondary to an acute reversible condition (untreated or uncontrolled hyperthyroidism, post- operative AF, fever, anemia)
9. Need for anti-arrhythmic therapy for a condition other than atrial fibrillation
10. Wolff-Parkinson-White syndrome
11. Any medical condition making compliance with study treatment unlikely
12. Current use of n-3 fatty acid supplements or use within the past 3 months
13. Pregnancy, breastfeeding, or possibility of becoming pregnant during the study (Patients must have adequate contraception as determined by the investigator),
14. Participation in another study at the same time or within 30 days of randomization.
15. Uncontrolled hypertension (systolic blood pressure > 180 mm Hg or diastolic blood pressure > 110 mm Hg
16. Suspected or known allergy to any ingredients in the study product or placebo, fish or shellfish .