Click on the links below to access all the ArticlePlus for this article.Please note that ArticlePlus files may launch a viewer application outside of your web browser.Intraoperative transesophageal echocardiography is a helpful monitoring device during cardiac surgery, but possible artifacts sometimes lead to critical misinterpretation. We experienced a rare artifact in a patient undergoing emergent mitral valve replacement.A 61-yr-old man (height, 165 cm; weight, 63 kg) with no previous medical history came to our hospital reporting dyspnea. Transthoracic echocardiography demonstrated papillary muscle rupture of the mitral valve and severe mitral valve regurgitation but otherwise no remarkable findings. Intraaortic balloon counterpulsation and percutaneous cardiopulmonary support had been established before the patient entered the operating room because blood pressure could not be maintained with continuous infusion of catecholamine. The flow of percutaneous cardiopulmonary support was approximately 3.8 l/min, and augmented systolic blood pressure was approximately 120 mmHg. Figures 1 and 2demonstrate transesophageal echocardiographic views of the aorta soon after induction of anesthesia. A high-echoic mass almost occupying the sinus of Valsalva was recognized. There was narrow retrograde blood flow through the center of the mass. (Additional information regarding this is available on the Anesthesiology Web site at http://www.anesthesiology.org.) At that time, no pathologic electrocardiographic change was observed. We considered it to be a large thrombus due to insufficient anticoagulation, so the aorta was incised immediately after conventional extracorporeal circulation was established. The surgeon inspected above and beneath the aortic valve; however, no thrombus could be found. The rest of the surgical procedure was uneventful, and the patient was discharged from the hospital without neurologic complication.In retrospect, it is speculated that the “mass” was displayed by the extremely stagnant blood flow in the sinus of Valsalva. No one present could insist confidently in the imminent situation that it was an artifact. We regret that we did not follow the image continuously until aorta incision.*Okazaki City Hospital, Okazaki, Japan. fukumotoke@m3.catvmics.ne.jp