This is the next ancient Chinese Healing Sound exercise, for the Heart, which in TCM understanding is understood as the seat of the mind and the control center for all qi-functions.
The sound associated with this exercise is "HU-AHH" or simply "HAAHH", which we only think in our imagination while we're exhaling the breath through the mouth.
This exercise belongs to the same set as the other Healing Sounds. With what we have learned up to now, the correct order for practice is:
Lungs, Liver, Spleen, Heart, San Jiao.