Pericardium. Congenital absence or partial pericardium is found throughout the world. In most cases, it has no clinical significance, but can show up incidentally as shifted heart on ct scans and xrays. In some folks there could be clinical significance if they need to undergo surgery. There are also some theories that the pericardium aids in the contraction or elastic recoil of the heart.
PARIETAL? You must have a typo and be asking about the parietal pericardium. It is an incomplete envelope the wraps around the heart: a thin membrane lining the closed cavities of the body; it has two layers with a space between that is filled with serous fluid.