The heart is covered by a two-layered pericardium. The outer part is called the fibrous coat and the inner part is called the serous coat. The serous membrane has two layers. Parietal layer and visceral layer. The outer layer is called the parietal layer and the inner layer is called the visceral layer. Between the two layers is the pericardial fluid. This fluid protects the heart from heat, pressure and friction injuries.