Enlarged left atrium causing possible false positive echocardiographic diagnosis of pericardial effusion.

Echocardiographic examination in a patient with IHSS, mitral insufficiency, and cardiomegaly suggested the possibility of a pericardial effusion. Echocardiographic M-mode scanning documented the continuity of the space posterior to the pericardium with an enlarged left atrium. Subsequent cineangiographic studies confirmed an enlarged left atrium and the absence of pericardial effusion. Left atrial enlargement may cause a false positive echocardiographic diagnosis of pericardial effusion.