The fourth Chakra is normally called the Heart Chakra in the West. In India there are many alternative name forms. You can find Anahat, Anahath, Anahatha and Anahada Chakra.
The central part of this chakra is associated with the immune system. It lies behind the STERNUM bone (breastbone) and close to the THYMUS gland, both of which play vital roles in the production of antibodies. So it is involved in the protection of the physical body.
On a psychological level, protection is also provided by the central part of the Heart Chakra. If it is in good order a person naturally feels secure and confident. There is no fear that the sky will fall in. If the chakra is weak a person is likely to feel insecure, perhaps even with sensations of tightness in the chest and lungs. It is a chicken and egg issue. External influences which cause insecurity will weaken the Centre Heart if they are sustained or severe. This is particularly true in the case of a child who has problems with his parents or who is not able to live with both parents.
When the Centre Heart of a woman is weak she is susceptible to breast cancer. One key contributor for a woman to develop a weak Centre Heart would be worrying about her husband, for example, because he is unkind or flirtish or unfaithful. Another cause could be that she, herself, is unkind or flirtish or unfaithful.
One technique to strengthen the Centre Heart is to recite the 23rd PSALM. This song or prayer instils a sense of confidence, the essence of which is that we are not alone and that we are positively helped by Divine forces. The benefit to the Heart Chakra is greater for a person who is meditating regularly and whose Kundalini has already been awakened.