pericardial effusion (PAYR-ih-KAR-dee-ul eh-FYOO-zhun)
A condition in which extra fluid collects between the heart and the pericardium (the sac around the heart). The extra fluid causes pressure on the heart. This keeps it from pumping blood normally. Lymph vessels may also be blocked, which can cause infection. Pericardial effusions may be caused by cancer or cancer treatment, infection, injury, autoimmune disorders, thyroid or kidney problems, or other conditions.