Floating thrombus in the aortic arch is an unusual source of systemic embolism. Surgical removal of the thrombus is a therapeutic option, because thrombolytic therapy carries the risk of partial lysis and repeat embolization. We report a case involving a large floating thrombus that originated in the proximal aortic arch and extended into the left subclavian artery and the descending aorta, and we discuss the surgical management.