I have also wondered exactly which place is regarded as the region of heart. Because, after we have sipped during Achamana we are required to touch the seven holes of the head as well as the seat of soul (as per Manu Smriti).
Now, the seat of the soul is said to be the region of heart in the Upnishads. So, is that region is on the left of our chest where the organ of heart resides or at the middle chest or somewhere else? We need to know this because we need to touch that spot.
We can get the precise location of this region from a minor Upanishad called MahAnArAyana Upanishad (MNU).
adho nishtyA vitastya ante (1) |
nAbhyAm upari tishthati (2)
hridayam tat vijAniya (3) |
vishvashya Ayatanam mahat (4)
That which is known as heart (3) is located above the navel (2), at
the distance of a finger-span (nishti) below the Adam's apple (vitasya
ante). This is the great abode ( Ayatanam) of the universe.
We precisely know where the Adam's apple is located in our throat so thus the region of heart is somewhere around the top portion of the middle of the chest.
The previous verse talks about a lotus that resides in that region (of heart) which one needs to meditate upon and this verse is precisely giving the location of the region.
The translation of 13.6 is as follows:
On the One who is limitless, unchanging, the supreme poet dwelling in
the sea (of one's heart) and the cause of the happiness of the works,
(one who should meditate). (The place for meditation is) the ether
(AkAsham) in the heart which is symbolised (pratikA) by an inverted
lotus bud (padma kosha).