Intraoperative transesophageal echocardiography (TEE) was used to monitor the removal of intracardiac masses in 17 patients. Prebypass TEE was used to confirm the preoperative diagnosis. It gave a clear image and anatomical definition of the mass in 16 cases. Moreover, in 11 of these patients, prebypass TEE provided information not obtained previously by traditional exams. This information was judged either useful or indispensable for a successful outcome in 10 of these patients. However, in one of the remaining six patients, TEE did not clearly visualize a flat thrombus in the left atrium. Postbypass TEE was used in each case to monitor the surgical results of the mass removal and the associated procedures. In one patient, it disclosed a progressively expanding hematoma in the left atrial wall, which was interfering with mitral valve function. From this experience, we consider intraoperative TEE the best monitoring device during cardiac mass removal because it usually provides a more complete diagnosis and anatomical definition of the mass than the traditional preoperative methods and permits monitoring of the surgical results before chest closure. Some limitations to this method may exist.