A 2-year-old girl presented with signs and symptoms of cardiac tamponade preceded by upper respiratory tract infection. A two-dimensional echocardiogram was suggestive of an intrapericardiac tumor. Exploration of the pericardium revealed a large amount of dense amber-colored "coagulated material." Microscopic examination of the material and the pericardium was diagnostic of acute pericarditis. Based on this experience we propose the term pseudotumor of the pericardium for this form of coagulated pus. We also propose that this term should be added to the differential diagnosis of intrapericardiac tumor.