interference with the venous return of blood to the heart due to an extensive accumulation of blood in the pericardium (pericardial effusion). Tamponade may occur as a complication of dissecting thoracic aneurysm, pericarditis, renal failure, acute myocardial infarction, hypothyroidism, autoimmune disease (for example lupus), chest trauma or a malignancy. Fluid in the pericardial sac is demonstrated by echocardiogram. Treatment involves the emergent removal of the fluid. This may be accomplished by a needle aspiration technique or emergency surgery (pericardial window).