The purpose of this study is to determine that a new drug called "Rivaroxaban®" is effective in preventing patients from forming clots after their heart rhythm has been reset by the cardiologist with an electrical device.

Patient who are electrically cardioverted require 1 month of anticoagulation (blood thinner). Rivaroxaban a Xa-inhibitor has been shown to be non-inferior to Warfarin (Vit K antagonist) the current standard of care in many treatment areas. Rivaroxaban will be compared to Warfarin historical control group studying the safety and efficacy in electrically cardioverted patients.

Inclusion Criteria:

• Patients with non-valvular atrial fibrillation requiring electrical cardioversion o Atrial fibrillation of unknown duration

Exclusion Criteria:

• Patients requiring extended anticoagulation after cardioversion due to concomitant risk factors as defined by CHADS2 score ≥ 1
• Significant renal dysfunction (CrCl <15mL/min)
• Significant hepatic dysfunction (Childs-Pugh Class B or C)
• History of coagulopathy
• Active bleeding
• Hypersensitivity to Rivaroxaban
• Concomitant use of anticoagulants
• Concomitant use of potent CYP3A4/P-gp inhibitors or inducers
• Interventions requiring interruption of therapy
• Pregnancy
• Age <18 y/o
• History of GI Bleed