The twelve petalled center is called the Heart chakra, and is placed behind the sternum bone in the spinal cord. This center corresponds to our cardiac plexus, which produces antibodies in infants until the age of twelve. The Heart chakra controls breathing by regulating the functioning of the heart and lungs.
When the kundalini pierces this center, we become an extremely confident, secure, morally responsible and emotionally balanced personality. Such a person is benevolent and loves humanity without any self interest involved, and is dear to all.
Within the Heart chakra resides the Self: the spirit, or atma. The spirit manifests when our heart is open, at which point we feel the pure joy of existence and the meaning and purpose of our place in creation. The quality of the Heart chakra is pure, unconditional love.