A transesophageal echocardiogram is a special technique for performing an echocardiogram which involves inserting an ultrasound probe down the esophagus of the patient.
A normal echocardiogram uses an ultrasound probe placed against the patient's chest (transthoraxic). However, the chest wall is very thick at this point and, as a result the images of the heart produced in this manner are not very clear. However, the heart is located very close to the esophagus, so the ultrasound penetrates further into the heart, providing clearer images.
However, a transthoraxic echocardiogram is a non-invasive procedure that is usually performed by a technician. Because of the complications in inserting the probe into the esophagus, the procedure must be performed by a physician on a patient who has not eaten, often by a surgical team, and takes longer. As such, a transesophageal is usually only performed once a problem, typically an embolism, has already been located in the heart in order to pinpoint its position. However, it's commonly performed as part of post-operative care on a patient who has had open-heart surgery.