Anahata, or Anahata-puri, or padma-sundara is symbolised by a circular flower with twelve vermillion, or green petals. (See also heartmind). Within it is a yantra of 2 intersecting triangles, forming a star of David, symbolising a union of the male and female. The seed mantra is Yam, the presiding deity is Ishana Rudra Shiva, and the Shakti is Kakini.
Anahata is related to the thymus, located in the chest. The thymus is an element of the immune system as well as being part of the endocrine system. It is the site of maturation of the T cells responsible for fending off disease and may be adversely affected by stress. . Anahata is related to the colours green or pink. Key issues involving Anahata involve complex emotions, compassion, tenderness, unconditional love, equilibrium, rejection and well-being. Physically Anahata governs circulation, emotionally it governs unconditional love for the self and others, mentally it governs passion, and spiritually it governs devotion.In Tibetan buddhism, this centre is extremely important, as being the home of the indestructible red/white drop, which carries our consciousness to our next lives. It is described as being white, circular, with 8 downward pointing petals, and the seed syllable Hum inside. During mantra recitation in the lower tantras, a flame is imagined inside of the heart, from which the mantra rings out. Within the higher tantras, this chakra is very important for realising the Clear Light.
Source - Wikipedia