Pericardium

the fibroserous membrane, consisting of mesothelium and submesothelial connective tissue, covering the heart and beginnings of the great vessels

Description
The pericardium is a closed sac having two layers: the visceral layer (epicardium), immediately surrounding the heart, and the outer parietal layer, forming the sac, composed of strong fibrous tissue, the fibrous pericardium, lined with the serous membrane, serous pericardium. Syn theca cordis, heart sac