Well some believe we have 7 major chakras in our soul. The heart chakra is the 4th and located around where your heart is. It is mostly associated with emotions and such but others say emotions come from the 5th chakra (throat chakra). The heart chakras colour is green.
Also like Divner said, it is an energy vortex like the other 6 chakras and in some beliefs can be used to absorb energy and direct energy out.