Blood in sac containing the heart.
The presence of blood within the membranous sac (pericardium) surrounding the heart, which may result from injury, tumors, rupture of the heart (e.g. following myocardial infarction), or a leaking aneurysm. The heart is compressed (cardiac tamponade) and the circulation impaired; a large fall in blood pressure and cardiac arrest may result. Surgical drainage of the blood may be life saving.