The pericardium is a double-walled sac containing the heart and the roots of the great vessels. The pericardial sac has two layers, a serous layer and a fibrous layer. It encloses the pericardial cavity which contains pericardial fluid. Human Pericardial Fibroblasts (HPcF) are the major cell type of the pericardium. They produce collagens and help form the thin but strong pericardium to serve as a protective sac. It provides structural support and lubrication, and also prevents excessive dilation of the heart. Constrictive Pericarditis involves activation and proliferation of pericardial fibroblasts, collagen and fibrin deposition, chronic inflammation, and scarring, where pericardium hardening eventually prevents the heart from expanding. Associations between fibroblast activation and immunomodulation make Pericardil Fibroblast cultures a useful tool for studying progressive sclerosing pericarditis.