The pericardium has many roles, the main three are to protect the heart, prevent the heart from dilating, lubricate and so on. 1. Protecting the heart: The pericardium is located on the outside of the heart and is a closed structure, so it can protect the heart from external pressure to a certain extent. At the same time, it can block some of the pathogenic bacteria, so it can reduce the risk of the heart being infected by pathogenic microorganisms. 2. Preventing heart dilatation: In general, the pericardium does not produce more obvious changes, if the heart is stimulated by changes in dilatation, the pericardium can prevent it from overexpansion, thus reducing the risk of excessive damage to heart function. 3. Lubrication: there is part of the plasma in the pericardium, in the normal beating process of the heart, the liquid in the pericardium can play a certain lubricating effect, prevent the heart from directly friction with the pericardium, reducing the risk of heart damage. The role of the pericardium also prevents the distortion of large blood vessels, assists and coordinates the interaction between the diastolic function of the right and left ventricles, maintains ventricular compliance, and negative pressure in the pericardial cavity during ventricular ejection facilitates atrial filling.