How do we define the spiritual heart?

TO BE COMPLETED from below References:

RAMANA http://www.sriramanamaharshi.org/teachings.html
In the center of the cavity of the Heart, the sole Brahman shines by itself as the Atman (Self) in the feeling of 'I-I'. Reach the Heart by diving within yourself, either with control of breath, or with thought concentrated on the quest of Self. You will thus get fixed in the Self.
NISARGADATTA
In seeking you discover that you are neither the body nor mind, and the love of the self in you is for the self in all. The two are one. The consciousness in you and the consciousness in me, apparently two, really one, seek unity and that is love.Q: How am I to find that love?
M: What do you love now? The 'I am'. Give your heart and mind to it, think of nothing else. This, when effortless and natural, is the highest state. In it love itself is the lover and the beloved
There is the material world (mahadakash) and the spiritual (paramakash). Between lies the universal mind (chidakash) which is also the universal heart (premakash). It is wise love that makes the two one.
Eternally the Great Heart beats and at each beat a new universe comes into being.
Do not undervalue attention. It means interest and also love. To know, to do, to discover, or to create you must give your heart to it -- which means attention. All the blessings flow from it.