This is how Dr. Bradley Nelson, the creator of The Emotion Code, explains the phenomena of the Heart-Wall.
The heart is the center of your being. It is through our heart that we give and receive love. Our heart is a center of our creativity, but our heart also is vulnerable to emotional injury. At some painful moments in our life we feel like our heart is going to break. When we are feeling deep grief, hurt, or loss our subconscious mind takes emotions trapped in the heart area, and literally makes a ‘wall’ around it. Why? To protect your heart from injury; to keep your heart from being totally broken.
When you realize that your mind puts up a heart wall to protect us, it all makes sense. If you have a Heart-Wall, you will have a harder time being able to give and receive love freely. The heart wall also hampers your ability to feel good emotions. It will contribute to feelings of isolation and depression, and further interfere with your ability to succeed. There are also physical effects of having a heart wall. It can cause heaviness/pain in the chest, neck, and shoulders. A heart wall will also lower your overall immunity.