The pericardium is not a lining of the heart. It is a a layer of connective tissue that surrounds the heart and the near ends of the large blood vessels. The heart is inside the pericardium.
All organs have such a connective tissue covering to protect and hold them. For the brain, it is called the meninges, and when it is inflamed, the condition is called meningitis.
This connective tissue is called fascia. Around organs it is called Visceral fascia.
Fascia also sounds your muscles (deep fascia). It helps keep the muscles in shape. When a muscle is injured, it tends to contract, because a muscle is strongest when it is contracted. The fascia will also contract to help hold the muscle in place. If the muscle doesnt move out that contracted state, the fascia will actually start to penetrate the space between the muscle fibers and harden the muscle, kind of like cement being poured into the muscle. This happens even with over-exercised muscles. Like you can have your shoulder muscles lock up with the fascia solidifying them. Therapeutic massaging causes the fascia to break up and be reabsorbed by the body, unlocking the muscle.