The serous fluid in the pericardial cavity
The pericardial fluid is the bodily fluid located in the pericardial cavity, and is secreted by the serous layer of the pericardium. The pericardium is a membranous sac containing the heart and is comprised of two layers (i.e. an outer fibrous layer and an inner serous layer).
The serous layer, in turn, is made up of two layers. These two layers are the parietal pericardium and the visceral pericardium. Both of these layers supply to the pericardial fluid. They secrete pericardial fluid into the space (referred to as pericardial cavity) between the two serous layers. This bodily fluid in the pericardial cavity lubricates the serous layers, allowing them to glide over each other with each heartbeat. 1 This reduces the friction during heart activity.
The pericardial fluid is said to contain high amounts of lactate dehydrogenase and lymphocytes although data on the normal range of the components of the pericardial fluid is still limited.2
1 Pericardial fluid. (n.d.). Britannica encyclopedia. Retrieved from http://www.britannica.com/EBchecked/topic/451651/pericardial-fluid.
2 Ben-Horin, S., Shinfeld, A., Kachel, E., Chetrit, A., & Livneh, A. (2005). “The composition of normal pericardial fluid and its implications for diagnosing pericardial effusions”. The American Journal of Medicine. 118 (6): 636–40