The serous pericardium of the heart is a sheet of mesothelial cells which lines, and so demarcates, the pericardial cavity. During development, where the layer has been invaginated by the heart, it comes to be divided into two:
- parietal layer of serous pericardium
- visceral layer of serous pericardium
It is important to emphasise that they are in continuity at the points at which great vessels traverse the pericardial cavity - the visceral pericardium envelopes the vessels - and only differ in the structures which they are superficial to. Both layers of mesothelial cells secrete the serous fluid which serves to lubricate the surface of the pericardial cavity.
The disappearance of the dorsal mesocardium during development leads to the formation of the oblique and transverse pericardial sinuses within the pericardial sac which separate the layers of serous pericardium.
There may be a small fold of serous pericardium joining the left pulmonary artery to the superior left pulmonary vein within the pericardial cavity. This is the fold of the left vena cava - it contains a fibrous remnant of the developmental left common cardinal vein.