Rivaroxaban vs. Warfarin for Post Cardiac Surgery Atrial Fibrillation

Inclusion Criteria: * Male or Female ≥ 18 years * At least one of the following procedures: coronary artery bypass grafting, aortic valve repair, mitral valve repair, non-mechanical aortic valve replacement, any combination of these procedures * Two or more episodes of New Onset Atrial Fibrillation (each lasting \> 20 minutes) or persistent atrial fibrillation lasting \> 24 hours (Or for \>18 hours over a 24-hour interval) * If female of child-bearing age, use of adequate contraception Exclusion Criteria: * Pre-existing paroxysmal atrial fibrillation before cardiac surgery * Pre-existing indications for therapeutic anticoagulation (Including but not limited to PE, DVT, mechanical valve) * Moderate-to-severe mitral valve stenosis not surgically corrected * Pre-existing allergy to study medications * Recent (\< 1 year) or ongoing pregnancy (Urine pregnancy test will be obtained for women of child bearing age at the time of enrollment into the study) * Stroke within 1 month prior to surgery or postoperatively prior to initiation of study drugs * Postoperative bleeding episode prior to initiation of study drug * Severe dysfunction of another organ system including GFR \< 30 ml/min, baseline INR \> 1.7, ileus or other gastrointestinal pathology hindering ability to absorb oral medications, and known coagulation pathway deficiencies * Postoperative need for non-aspirin anti-platelet therapy that cannot be discontinued when therapeutic anticoagulation is initiated * Patient takin…