The left atrial appendage(LAA)is the most common site of left atrial thrombus with more than 90％of thrombi formed within this structure.[1]Transesophageal echocardiography(TEE)is the gold standard imaging technique for identifying LAA thrombus,with sensitivity and specificity both of 95％-100％.[1,2]An imaging mod-ality that is used on most cardiac patients is the transthoracic echocardiogram(TTE).While quick and noninvasive,it is not known for its ability to detect left atrial appendage thrombi.Detecting a thrombus on TTE is a great advantage as it allows for rapid initiation of anticoagulation and avoid-ance of cardioversion early in atrial fibrillation pa-tients.This case demonstrates the rare occurrence of a patient who was found to be in atrial fibrillation in the setting of thyrotoxicosis who was sub-sequently discovered to have a left atrial append-age thrombus on TTE.