Transesophageal echocardiography is a safe, minimally invasive procedure that should be considered when the diagnosis of cardiac tamponade is a possibility and when conventional methods fail to provide conclusive diagnostic information. In this report, we describe a 74-year-old man in the intensive-care unit whose condition was unstable postoperatively because of an occult loculated pericardial effusion and cardiac tamponade. Routine noninvasive and invasive monitoring, including hemodynamic monitoring and transthoracic echocardiography, failed to confirm definitively the suspected diagnosis of cardiac tamponade. In addition, because of the hemodynamic instability of the patient, transporting him for definitive tests (such as fast computed tomographic scanning of the mediastinum, which could not be performed at the bedside) for assessment of cardiac tamponade was relatively contraindicated. In our patient, the diagnostic information obtained by transesophageal echocardiography may have been lifesaving.