This study will enroll people who have had at least two occurrences of AF. Participants will be randomly assigned to receive either fish oil supplements or placebo for 24 weeks. At study visits at baseline and Weeks 2, 4, 8, 12, 18, and 24, participants will undergo a medical and social history review, a physical exam, and blood and urine collection. At the baseline study visit, an electrocardiogram will also occur.