To describe the role of transesophageal echocardiography (TEE) in the diagnosis of various cardiac pathologic conditions, we reviewed the currently accepted clinical applications, the contraindications to the procedure, and the potential complications. The Mayo Clinic experience with 7,134 TEE examinations during a 6-year period (1988 through 1993) was summarized, and TEE results reported in the literature were reviewed. TEE has a substantially higher yield than transthoracic echocardiography (TTE) for diagnosis of direct and indirect sources of cardioembolism. Moreover, TEE is highly sensitive for detecting abnormalities of mitral prostheses and endocarditis-related complications of aortic prostheses. TEE is superior to TTE for localization and characterization of cardiac and paracardiac masses. In addition to establishing the diagnosis of aortic dissection, TEE can readily show the site, type, and extent of the tear. Ventilated, critically ill patients can safely undergo TEE. TEE has a limited role in the assessment of neonates, infants, and children with congenital heart disease because TTE can provide almost all the necessary information in such patients. Intraoperatively, TEE is useful for managing patients undergoing mitral valve repair and for monitoring for air and fat embolism in those undergoing neurosurgical procedures or hip replacement. Absolute contraindications to the performance of TEE include a history of dysphagia, current pathologic conditions of the esophagus, and recent esophageal operations. In patients with relative contraindications, such as esophageal varices or active upper gastrointestinal bleeding, the risk-to-benefit ratio must be assessed before TEE is performed. Complications associated with TEE can be related to the probe, to the procedure, or to drugs used during the examination.(ABSTRACT TRUNCATED AT 250 WORDS)