A Broken or Pierced Heart, and a Contrite Spirit
There seems to be a duality between a hardened heart and a broken heart. The hardened heart is egoism, thinking and feeling as if we are separate from everything else, alone, and creating a need to compete, fight, and save ourselves. The open heart is when we can see that we are connected to everything and everyone else, creating a need to fulfill a bigger picture. A hard heart likens us to a single celled organism, while a broken heart makes us a functional cell in an entire body.
Zohar 68a-69a: Why the Animal was Destroyed by the Deluge
A translation of an exert from the Zohar.