In ullladu narpadu anubhandam of Ramana Maharshi,
Verses 18 to 24 are about the subject of the ‘heart’, a term that in a spiritual context means the innermost core or essence of our being. Ramana Maharshi had translated some of these verses from the Malayalam version of Ashtanga Hridayam and the rest from Yoga Vasistha.
Verses 18 and 19 describe it as being like a lily bud located within our chest, ‘two digits to the right’, and say that in the tiny hole inside its closed mouth the darkness (of self-ignorance) exists along with desire and other passions; that all the major nadis (subtle channels through which consciousness and prana flow) depend upon it; and that it is the abode of the light (of consciousness), the mind and the prana (life-force).
A more detailed description is given in the Ramana Gita in the fifth chapter as recorded by Kavyakantha Ganapathi Muni.
prAgukte.abde.aShTame mAsi navame divase nishi | upanyasitavAn
saMyaguddishya hR^idayaM muniH || 1||
nirgachChanti yataH sarvA
vR^ittayoH dehadhAriNAm | hR^idayaM tatsamAkhyAtaM
bhAvanA.a.akR^itivarNanam || 2||
ahaMvR^ittiH samastAnAM vR^ittInAM
mUlamuchyate | nirgachChanti yato.ahandhIrhR^idayaM tatsamAsataH ||
hR^idayasya yadi sthAnaM bhavechchakramanAhatam | mUlAdhAraM
samArabhya yogasyopakramaH kutaH || 4||
raktapiNDAdadR^idayamuchyate ayaM hR^iditi vR^ittyA tadAtmano
rUpamIritam || 5||
tasya dakShiNato dhAma hR^itpIThe naiva vAmataH |
tasmAtpravahati jyotiH sahasrAraM suShumNayA || 6||
sahasrArAttadA lokAnubhUtayaH | tAH prapashyan vibhedena saMsArI
manujo bhavet || 7||
In the aforesaid Year, on the night of the ninth of August , Ramana Muni spoke exhaustively regarding the Heart. 5.1
ÒThat from which all thoughts of embodied beings issue forth is called
the Heart. All descriptions of it are only mental concepts. 5.2.
The ÔIÕ-thought is said to be the root of all thoughts. In brief, that
from which the I-thought springs forth is the Heart. 5.3.
This Heart is different from the blood-circulating organ. ÔHridayamÕ
stands for hrit Ôthe centre which sucks in everythingÕ, and ayam
ÔthisÕ and it thus stands for the Self.
The location of this Heart is on the right side of the chest, not at
all on the left. The light (of awareness) flows from the Heart through
sushumna to sahasrara 5.6
From there, it flows to the entire body, and then all experiences of
the world arise. Viewing them as different from the Light, one gets
caught up in samsara 5.7.
The whole universe is in the body and the whole body is in the Heart.
Hence all the universe is contained in the Heart. 5.11.
The notion that the seer is different from the seen is only in the mind. For those that abide in the Heart the seer and the seen are one. 5.19