 Accurate determination of the presence or absence of left atrial appendage LAA thrombus has a large impact on the clinical course of patients with atrial fibrillation or ischemic stroke and has large financial implications as well. Misdiagnosing the presence of LAA thrombus can lead to unnecessarily cancelled procedures cardioversion and atrial fibrillation ablation and potentially hazardous, unnecessary changes in clinical care such as prolonged Coumadin anticoagulation. Missing LAA thrombus can result in continuation of cardioversion or atrial fibrillation ablation procedures at a time when there is higher risk of subsequent embolic stroke. 