Transesophageal echocardiography (TEE) is a Doppler technique that uses the esophagus as an acoustic window. In critically ill patients (particularly ventilated patients), TEE may be used to assess left ventricular function, valvular disease, endocarditis, and prosthetic valve dysfunction. It is also helpful in elucidating the cause of hypotension after cardiac surgery, and can detect chronic aortic dissection and transection, valve rupture, and myocardial contusion in trauma victims. TEE is superior to transthoracic echocardiography in evaluating a cardiac source of embolism. Contraindications to TEE include esophageal disorders and an uncorrected bleeding diathesis; a large hiatal hernia may cause suboptimal transgastric images.