Exploring the Efficacy of Once Daily Oral Rivaroxaban for Treatment of Thrombus in Left Atrial/Left Atrial Appendage in Subjects With Nonvalvular Atrial Fibrillation or Atrial Flutter

Inclusion Criteria: * Men or women aged \>/= 18 years * Hemodynamically stable nonvalvular AF or atrial flutter * LA/LAA thrombus documented at baseline by transesophageal echocardiography (TEE) up to 72 hours prior to start of study medication * vitamin K antagonist(s) (VKA)/ new oral anticoagulant(s) (NOAC)-naïve or untreated within 1 month prior to signing of the informed consent form * VKA pretreated but under ineffective INR levels(\<2.0,documented with at least 2 consecutive measurements that are at least 24 hours apart) within last 6 weeks * Women of childbearing potential and men must agree to use adequate contraception when sexually active Exclusion Criteria: * Transient Ischemic Attack within 3 days prior to study inclusion * Severe, disabling stroke (modified Rankin score of 4-5, inclusive) within 3 months or any stroke within 14 days before the start of study drug * Acute thromboembolic events or thrombosis (venous/arterial) within the last 14 days prior to study inclusion * Acute myocardial infarction within the last 14 days prior to study inclusion * Cardiac-related criteria: Previous intracardiac thrombus, Free-floating ball thrombus, Intracardiac tumor, known left ventricular or aortic thrombus * Active bleeding or high risk for bleeding contraindicating anticoagulant therapy * Concomitant drugs/therapies: Indication for anticoagulant therapy for a condition other than nonvalvular AF or atrial flutter (eg, venous thromboembolism). Concomitant use of anticoagulant drugs, including VKA, or factor IIa or factor Xa inhibitors. Chronic aspirin therapy \>100 mg or dual antiplatelet therapy. Concomitant use of strong inhibitors of both cytochrome P450 (CYP) 3A4 and P glycoprotein (P-gp), ie, all human immunodeficiency virus protease inhibitors and the following azole antimycotics agents-ketoconazole, itraconazole, voriconazole, and posaconazole-if used systemically * Concomitant conditions: Childbearing potential without proper contraceptive measures, pregnancy, or breast feeding. Hypersensitivity to investigational treatment. Calculated creatinine clearance (CrCl) \< 15 mL/minute at the screening visit. Hepatic disease which is associated with coagulopathy leading to a clinically relevant bleeding risk. Any severe condition that would limit life expectancy to less than 3 months (eg, advanced malignancy, etc.). Planned invasive procedure with potential for uncontrolled bleeding or increased risk of stroke, including major surgery, cardiac catheterization, or cardioversion prior to the end-of-treatment TEE. Inability to take oral medication. Ongoing drug addiction or alcohol abuse