When patients present with suspected prosthetic valve dysfunction, investigation is usually instituted to delineate the site and cause thereof. Precordial cross-sectional echocardiography is often helpful in this respect, but in the patient with acute pulmonary edema, imaging may be impaired because of discomfort and respiratory distress. The information obtained may also be suboptimal as a result of concomitant obesity, chest wall deformity, and pulmonary disease. In addition, further difficulties may relate to the acoustic shadowing produced by the metallic portion of the valve and its sewing ring, especially with valves in the mitral position. In such patients, cardiac catheterization may cause further decompensation and is associated with a recognized increase in morbidity and mortality. Angiography does not accurately site regurgitant jets in relation to the prosthetic valve concerned and will not detect the presence of vegetations. Transesophageal echocardiography circumvents many of these imaging difficulties and we evaluated its use in five patients with prosthetic heart valves who presented acutely ill, in severe pulmonary edema and suspected prosthetic heart valve failure. In each case, the diagnosis of valve dysfunction was established, and precise information regarding the site and cause of the failure was obtained. No complications or deterioration in patient condition resulted from the procedure and the findings were confirmed at surgery performed within 24 hours in all five patients. Transesophageal echocardiography should be included in the assessment of acute prosthetic heart valve failure.