Subserosa of pericardium

The subserosa of the pericardium, also known as the submesothelial connective tissue layer, is the thin layer of loose connective tissue that lies immediately beneath the mesothelial (serosal) layer of the serous pericardium. It forms part of the histological composition of both the parietal and visceral layers of the serous pericardium.

This layer contains a delicate network of collagen and elastic fibers, fibroblasts, mast cells, and macrophages, along with small blood vessels, lymphatic capillaries, and nerves that support the overlying mesothelium. The subserosa provides structural support, mechanical flexibility, and a pathway for vascular and neural elements traversing between the fibrous pericardium and the mesothelial surface.

Histologically, it corresponds to the submesothelial space described by Ishihara et al. (1980) in the parietal pericardium and is homologous to subserosal layers found in other serous membranes (e.g., pleura and peritoneum).