8. History of paroxysmal (intermittent) atrial fibrillation will be considered an exclusion. Patients with persistent atrial fibrillation as defined by continuous atrial fibrillation for at least 6 months and controlled with a rate control strategy (i.e., selective beta blocker, calcium channel blocker, pacemaker placement, digoxin or ablation therapy) for at least 6 months may be considered for inclusion. In such patients, heart rate at enrollment must be < 100/min.