Pericardial effusion ("fluid around the heart") is an abnormal accumulation of fluid in the
pericardial cavity. Because of the limited amount of space in the pericardial cavity,
fluid accumulation leads to an increased intrapericardial pressure which can negatively affect
heart function. A pericardial effusion with enough pressure to adversely affect heart function is called
cardiac tamponade. Pericardial effusion usually results from a disturbed equilibrium between the production and re-absorption of
pericardial fluid, or from a structural abnormality that allows fluid to enter the pericardial cavity.