Because it is sometimes difficult to determine the cause of hypotension in patients after cardiac operations, we assessed the value of transesophageal echocardiography in this respect, and we studied 60 consecutive patients who had hypotension despite positive inotropic medication and, in some patients, mechanical support. Echocardiographic diagnoses were compared with diagnoses based on hemodynamic parameters. Follow-up examinations were completed in all patients to confirm the final diagnoses. Echocardiographic signs of hypovolemia were present in 14 patients, tamponade in six, left ventricular failure in 16, right ventricular failure in 11, and biventricular failure in eight. Echocardiographic examination proved to be inconclusive in five patients. Comparison with hemodynamic parameters showed agreement on diagnoses (hypovolemia versus tamponade versus cardiac failure) in 30 patients (50%). Echocardiography correctly identified two patients with tamponade and six with hypovolemia; these conditions were not suspected by standard hemodynamic data; in five patients unnecessary reoperation was prevented, although hemodynamic values were suggestive of tamponade. Echocardiography also identified subcategories of patients at high risk of death (those with signs of right ventricular and biventricular failure). These findings suggest that transesophageal echocardiography performed on patients after cardiac operations, at the bedside in the intensive care unit, can readily elucidate the cause of hypotension in the large majority of patients and is a valuable adjunct to hemodynamic evaluation in patient management. Furthermore, it appears to be possible to identify subcategories of high-risk patients, based on these echocardiographic findings.