A 60-year-old white man became hypotensive and dyspneic 3 days after right pneumonectomy for bronchogenic carcinoma. Transthoracic echocardiography was nondiagnostic because of technical difficulty. Transesophageal echocardiography demonstrated a loculated posterior pericardial effusion with isolated diastolic left atrial collapse. The hemodynamic disturbance resolved after drainage of the effusion. Transesophageal echocardiography plays a valuable role in the diagnosis of postoperative cardiac tamponade.