The |heart| has a covering as well as a lining, the |pericardium|, consists of two layers of fibrous tissue with a small space in between. The inner layer covers the |heart| like a layer of skin, but the outer layer is much looser, allowing room for the |heart| to beat. A thin layer of pericardial film fills the space between the two layers and acts as a lubricant between the |heart| and its enveloping sac. It also supports the |heart| and cushions it as it beats.
