|A transverse section of the thorax, showing the contents of the middle and the posterior mediastinum. The pleural and pericardial cavities are exaggerated since normally there is no space between parietal and visceral pleura and between pericardium and heart.|
The serous pericardium is deeper than the fibrous pericardium in the heart. It contains two layers, both of which function in lubricating the heart to prevent friction from occurring during heart activity:
- The layer adherent to the fibrous pericardium is the parietal layer.
- The layer deep to the fibrous pericardium is the visceral layer. When this layer comes into contact with the heart (not the great vessels), it is known as the epicardium.
The serosal pericardium is a single layer of flat cell lying on a subserosal layer of connective tissue. The subserosal layer fuses with the fibrous pericardium in the parital membrane and it fuses with the myocardial tissue in the visceral membrane. The serousal layer is on the subseroal layer so it faces the pericardial cavity and it possibly secretes the pericardial fluid.
Together these two layers form a continuous uninterrupted membrane. Between these two layers exists a small cavity called the pericardial cavity, which contains a supply of serous fluid. The serous fluid that is found in this space is known as the pericardial fluid.
Additional Images 
- thoraxlesson4 at The Anatomy Lesson by Wesley Norman (Georgetown University) (heartpericardium)
- Atlas of anatomy at UMich ht_pericard1 - "Chest X-ray showing pericardium, posteroanterior view"
- Atlas of anatomy at UMich ht_pericard2 - "MRI of chest, lateral view"