This is not the pericardium itself. It is a matrix of connective tissue created by excretions from the heart cells. Created by chemically "washing out" the other cellular material, this heart housing may potentially be used to grow another heart.
Doctors take healthy cells from the same individual and "install" them into this housing. The healthy cells could use the matrix to re-grow into a functional heart which could be transplanted without risk of rejection to the original source individual.
This matrix is also linked to the surrounding fascia/CT of other organs and, of course, the lines running through the chest. This image really helps to hammer home the concept of each piece of the body relating via the fascial web.
There is more than one way to pull on the heart strings.