This heart is indeed the location of the very Atman.
Note by R. Ganapthy, the collator of these discourses: Shri Ramana Maharishi used to say: “The (spiritual) heart, which is the location of the Atman is within the right chest of a jIva”
Of course it is true that the Atman is permeating everywhere in such a way that there is no space for ‘space’ and so no ‘location’ to be specified for the Atman.
The words ‘sarvaM’ (all) and ‘vyApakaM’ (permeation) both need for their meaning the concept of space, but it is true that space itself is subsumed by the Atman as to be nowhere.
However, for the mind (antaH-karaNaM) which is always drawn towards duality, to be turned to non-duality by the Grace of God, and towards meditation of the Atman, it needs some kind of a prop, at least mentally.