This trial will randomize 250 patients presenting to the Mayo Clinic Cardioversion Unit over one year to two groups including a mangosteen supplemented group versus a control group with placebo juice. Patients will be enrolled who have a history of paroxysmal, persistent, or longstanding persistent atrial fibrillation and excluded if they have a history of recent surgery, myocardial infarction, infection, collagen vascular disease with active inflammation, or thyroid disease. Furthermore, patients already on corticosteroids will be excluded. Patients will be evaluated at enrollment and followed at 3 months and 6 months with repeat ECG, laboratory testing of inflammatory biomarkers and endothelial function, as well as quality of life questions.