Cardiac tamponade by loculated pericardial hematoma: limitations of M-mode echocardiography.

Three patients developed cardiac tamponade after heart surgery. Pericardial effusion was not identified by M-mode echocardiography. Two patients underwent two-dimensional echocardiography which showed compression of the right atrium by a localized mass. At reoperation, atrial compression by a loculated effusion or hematoma was found and successfully relieved. When cardiac tamponade is suggested by the clinical setting, but not supported by M-mode echocardiography, the presence of a loculated effusion should be considered and evaluated by a two-dimensional echocardiographic study.