With the color of pink the gemstone most often associated with the heart chakra is the Rose Quartz, however peridot can also be used to balance this chakra. The Endocrine gland associated with the heart chakra is the thymus. This gland, although technically part of the endocrine system is more often related to the immune system since it is where the cells that help us fight infections, namely T cells, mature. This gland is also a regulator/balancer as we grow to help us to fight off sickness and to build up our immune system as we grow.
The central issue of the Heart Chakra is love and relationships. It is where we build up our self acceptance through balance, compassion and good relationships. Our motives and rights here are to love and be loved and we identify with the social aspects of our lives. Our demon, that which can make us "sick" at this chakra is grief. The loss of love or a loved one affects this chakra deeply.
When this chakra is in excess there is codependency, poor boundaries, possessiveness and jealousy. When this chakra is deficient the person may be shy, lonely or isolated. Additional problems when the heart chakra is deficient could be bitterness and a lack of empathy. When the heart chakra is deficient the person may also have a critical nature as love is lacking in their life.
This chakra's main emotions deal with love, relationships and the social aspects of each. It also balances the chakras above and below.