Assessment of Cardioversion Using Transesophageal Echocardiography II (ACUTE II)

Inclusion Criteria: Patients with chronic or paroxysmal atrial fibrillation of > 2 days duration who are candidates for early chemical or electrical cardioversion Patients with atrial flutter with a documented history (electrocardiography) of atrial fibrillation Males and females 18 years of age or older Patients have available results of routine clinical labs for standard clinical chemistry and complete blood count within the previous 14 days Exclusion Criteria: An INR > 1.4 in patients who have received warfarin prior to enrollment. Use of IV heparin for more than 72 hours immediately prior to randomization. Patients with contraindications to TEE, such as dysphagia, or esophageal strictures. Patients who will need anticoagulation discontinued because of elective intervening procedure, such as cardiac catheterization or surgery. Patients with contraindications to warfarin or heparin Patients who require concomitant therapy during the study period with any drug known to affect coagulation or platelet function (i.e. ASA, NSAID, antiplatelet drugs) Women of childbearing potential, unless pregnancy can be excluded by medical history incompatible with pregnancy or by serum or urine beta HCG levels. Patients who are hemodynamically unstable and thus may require immediate cardioversion. Weight less than 40 kg (88 pounds) or more than 125 kg (275 pounds) History of gastrointestinal bleeding disorder and/or endoscopically verified ulcer disease within the last year History of intracranial or retinal bleeding, or other known disorders with an increased risk of bleeding Ischemic stroke in the previous three months Uncontrolled hypertension (systolic blood pressure greater than 180 mm Hg or diastolic blood pressure greater than 100 mm Hg) Malignancy currently under active treatment, including melanoma Patients with renal insufficiency (creatinine > 2.0 mg/dL) or are renal transplant subjects Patients with anemia (Hgb less than 10 gm/dL) Patients with thrombocytopenia (platelet count less than 100 x 10^9/L) Positive fecal hemoglobin test Life expectancy of less than 6 months History of drug and/or alcohol abuse within the last two years Patients unable or unwilling to give informed consent Patients unable or unwilling to return for follow-up Prisoners or wards of the state Patients with psychological problems that may decrease compliance with the protocol Not willing to complete the Quality of Life Questionnaires x 3 Participating in another clinical trial and/or taking an investigational medication in the past 30 days Patient language, learning skills, or home environment unconducive to self-management