Stroke is one of the most common causes of death; in particular, cardiac source of embolism may be responsible for 15-20% of ischemic strokes. Here we report a case of left atrial thrombus diagnosed by transesophageal echocardiography (TEE) immediately after induction of general anesthesia in a patient with infarction of the middle cerebral artery. In this case, an emergent craniectomy was cancelled and medical treatment was performed. This case report shows that TEE taken in the operating room may play an important role in the change of treatment plan in a patient displaying acute mental change.