Hypothesis 2: That ICE can identify low risk patients in whom immediate cardioversion during the procedure is safe and comparably effective to electrical cardioversion performed based on a conventional strategy of a minimum of 3 weeks of preceding anticoagulation therapy. Low risk patients are expected to have an acceptably low incidence rate of stroke, transient ischemic attack (TIA), peripheral embolism, and major hemorrhagic events following electrical cardioversion. This will be evaluated during the Phase II component of the study, after the Phase I objective is achieved.