I think these texts speak for themselves. They speak about the heart within each of us.
Within the soul there exists a hidden chamber which is outside time and space, and which transcends that part of the soul giving life and movement to the body. It is within this hidden chamber that we encounter divinity; it is there that we become utterly still, totally true to ourselves, completely detached from all material concerns.
The atmosphere within that chamber is pure; within that chamber you are free from all bonds. God dwells, acts and rules within that chamber. Entering that chamber cannot be compared with any other aspect of your life, even the most devout religious observance. There you are united with God; there the fire of His love burns, and you are consumed by it.
Johann Tauler - Christian Mystic. Written during the 14th Century CE, Germany
Within the city of Brahman, which is the body, there is the heart, and within the heart there is a little house. This house has the shape of a lotus, and within it dwells that which is to be sought after, inquired about, and realized. What then is that which, dwelling within this little house, this lotus of the heart, is to be sought after, inquired about, and realized?
As large as the universe outside, even so large is the universe within the lotus of the heart. Within it are heaven and earth, the sun, the moon, the lightning, and all the stars. What is in the macrocosm is in this microcosm. All things that exist, all beings and all desires, are in the city of Brahman; what then becomes of them when old age approaches and the body dissolves in death?
Though old age comes to the body, the lotus of the heart does not grow old. At death of the body, it does not die. The lotus of the heart, where Brahman exists in all his glory—that, and not the body, is the true city of Brahman. Brahman, dwelling therein, is untouched by any deed, ageless, deathless, free from grief, free from hunger and from thirst. His desires are right desires, and his desires are fulfilled.
From the Chandogya Upanishad. Written before the 8th century BCE, India