Normal Fluid level in the pericardial cavity:

The visceral layer is closely applied to the hea and is often called the epicardium.The slitlike space between the parietal and visceral layers is referred to as the pericardial cavity.Normally, the cavity contains a small amount of tissue fluid (about 50 mL), the pericardial fluid, which acts as a lubricant to facilitate movements of the hea.