In this study we chose to look at patients undergoing cardioversion. This is because this group has a high likelihood of recurrence of AF and would benefit most by an effective drug. Once the decision is made to have the patient undergo cardioversion, we will approach the patient about enrolling in this trial. The only change in their medical therapy will be the addition of the study drug. The study requires no other alterations to the standard of care. If patients agree to participate, then they will be started on the study drug and followed for recurrence of AF by a variety of surface electrocardiogram techniques. All of which are noninvasive. To insure the medicine is not causing side effects, examinations and blood tests will be done, and to study whether the drug actually affects oxidative stress, blood will be analyzed. The subjects participation ends when AF recurs or after 1 year. This will be a double blind, placebo controlled trial and will be analyzed on an intention to treat basis.