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Function [edit]. The pericardial fluid reduces friction within the pericardium by lubricating the epicardial surface allowing the membranes to glide over each other with each heart beat.
The pericardium is in the thoracic cavity and partially surrounds the heart. The heart is also supported by parietal and visceral pericardium. These all are serous membranes. Serous membranes secrete a watery fluid that lubricates and helps minimize friction between organs and membranes.