The fluid present between the two layers of pericardium is called pericardial fluid. It saves our heart from small mechanical injuries.
There is a very small amount of fluid called pericardial fluid in the pericardial sac. This fluid helps to decrease friction between the pericardial layers. It also allows for smooth movement of the heart when it beats.
Normally, there is a small amount of fluid between them. The fluid reduces friction between the two layers as they rub against each other during each heartbeat. In some cases, extra fluid can build up between these two layers leading to a pericardial effusion. A little fluid won't cause much of a problem.
Normally there is between 10–50 ml of pericardial fluid.
Causes of pericardial effusion include: Inflammation of the pericardium following heart surgery or a heart attack. Autoimmune disorders such as rheumatoid arthritis or lupus. Spread of cancer (metastasis), particularly lung cancer, breast cancer, melanoma, leukemia, non-Hodgkin's lymphoma or Hodgkin's disease.