Question

Why heart is covered with pericardial membrane

Answer 1

The pericardium membrane is smooth and acts as a cushion, it protects the  heart so that bones of rib could not damage the heart when it contracts.

Answer 2

The pericardial sac has two layers, a serous layer and a fibrous layer. It encloses the pericardial cavity which contains pericardial fluid. The pericardium fixes the heart to the mediastinum, gives protection against infection and provides the lubrication for the heart.