What is the bija mantra for the Anahata Chakra and how should it be used?

The bija (seed) mantra of the Anahata Chakra is YAM — the seed sound of the Vayu (air) element and the vibrational essence of the heart centre. To use it: sit comfortably, place both hands gently over your heart centre in Hridaya Mudra. Close your eyes and take a few deep breaths, relaxing the chest. On each exhale, chant a long resonant YAAAA-MMM, feeling the vibration spreading across the chest cavity. Practice 21 or 108 repetitions daily. The key is sincere intention: the quality of heart present in the practice matters infinitely more than perfection of pronunciation.