The great difficulty here is that there isn't one!
Probably the best explanation of the importance of Heart Energy comes not surprisingly from one of India's greatest sages, who without doubt exemplified it's qualities and wisdom throughout his lifetime.
‘THE HEART IS THE CENTRE OF ALL’
by Sri Ramana Maharshi (1879- 1950)
Just as there is a cosmic centre from which the whole universe arises and has its being and functions with the power or the directing energy emanating therefrom, so also is there a centre within the frame of the physical body wherein we have our being. This centre in the human body is in no way different from the cosmic centre. It is this centre in us that is called the Hridaya, the seat of Pure Consciousness, realized as Existence, Knowledge and Bliss. This is really what we call the seat Consciousness or God in us.
It is this Hridaya or Self that is said to be different from the physical heart, regulating the blood circulation. The Hridaya has its being on the right side and is not commonly known or felt. The primary thought in us arising as 'I,' when traced to its source, ends somewhere in us and this place, where all thoughts die, where the ego has vanished, is the Hridaya. From this centre is felt and enjoyed the Pure Consciousness.
Hridaya described as 'the literal, actual, physical seat of the intuition of the Self' has the meaning explained above. Perhaps the words 'physical seat' may create some confusion. What it really means is that there is a centre of Pure Consciousness in the physical body. It is related to the physical, but is not itself physical.
The word Hridaya is a composite of hrid and ayam - "centre, this". It is the centre on the right which we reach as a result of meditation. From the Hridaya, consciousness arises to the sahasrara through the sushumna and from there spreads out to all the parts of the body through the several 'nadis'. Then alone we become conscious of the objects around us. Man, due to the illusion that these have real existence, experiences suffering, as he strays far away from his Self. The seat from where all these arise and manifest is the Hridaya.