Bhagavan Ramana is quoted in https://hridaya-yoga.com/hridaya-yoga-articles/what-is-hridaya-the-spiritual-heart/.
According to Ramana Maharshi, the great Advaita master, “The godly atom of the Self is to be found in the right chamber of the heart, about one finger-width’s distance from the body’s midline. Here lies the Heart, the dynamic Spiritual Heart. It is called hridaya, is located on the right side of the chest, and is clearly visible to the inner eye of an adept on the Spiritual Path. Through meditation you can learn to find the Self in the cave of this Heart."
When we withdraw the senses (pratyahara) and center ourselves in the chest area, looking for the deepest aspects of our being, we start to search “the interior” to the detriment of “the exterior.” In this way, we pass from the usual “conquering” attitude of the mind to a receptive, contemplative disposition. It is a kind of surrender, which implies lucidity, discernment, vigilance.
In Christian spirituality, entering the heart consummates the divine and the human.
In the domain of the Heart, most of us are somewhat or entirely illiterate. “The intellect of the Heart” does not function by formulating abstract concepts and does not reach conclusion through deductive reason. It understands Divine Truth by means of immediate experience or intuition. We "understand clearly that the essential awareness of our own being is not a function of reason. It is not the mind or a product of the mind, nor is it ordinary thoughts, but it is a radiance emanating from the region of the chest." We just need to watch this radiance.
The Heart knows through surrender, trust, and joy. Coming back to the Heart, all the vain noise of the world is quieted. The Heart is a sanctuary of silence. There, in the most sacred intimacy and solitude of the “cave of the Heart”, the moods of individuality fade away and the consciousness of unity is revealed. There, the world and man are one. So, in a paradoxical way, the solitude and intimacy of the Heart reveals the essential Unity of all existence.
Swami Ramakrishnananda quotes Sri Ramakrishna: "As long as man remains outside the lotus of his heart he has to wander in search of pleasure in vain, but once he goes inside it and tastes the nectar of divine communion; all his wanderings cease once for all. Realizing God in the heart he is in a state of bliss." "What indescribable bliss comes to him when his soul is in direct communion with God!", he asks. Rohit Mehta writes in "The Creative Silence", The Theosophical Publishing House, 1957, "Reality always is, it has not to be brought into existence. Because there are screens hiding reality," we do not discover it. "It is only as veil after veil is rent asunder that the reality comes to view", exactly what Agathiyar and Ramalinga Adigal mentioned to us too. This path is not of finding something anew or a path of discovery. It is an unveiling of something that is already there. Once we see our true nature we are enlightened the very moment. When many pay to attend classes that teach how to open the heart, as Tavayogi used to say that we got to come into the company of the Siddhas quite easily, without the hardship that he and many others went through, the heart chakra was opened by the divine itself, asking only one thing from us - that we surrender to him. We are blessed indeed. All these is possible only by the grace of our Gurus, through masters both ascended or unascended as Djwal Kul says and the consent of the divine.
After having hibernated in the dark dungeons and caves or Kugai of the heart chakra, Agathiyar, our Parama Guru came within the confines of our hearts that was the abode of Kuga (Lord Muruga), bringing in the light of knowledge and illuminating the space, to reveal the magnificent splendor and majesty and golden hue of Lord Muruga, the embodiment of Gnana. Lord Muruga himself on his part came through a devotee and told us that he was giving us something that day after we had conducted puja at the home of a devotee. He strictly told us that only those who had surrendered should step up and hold his hands to receive his initiation. Before he could give us that which he had come to give, he asked us to open our hearts and let him in. To those who held on, he asked them to let go. As we all stood in line to receive the initiation from Lord Muruga again he asked of us if we had surrender completely. Only after getting us to drop all fears and doubts and after we committed wholeheartedly in opening up our hearts, did he come within to take his dwelling. There was no mantra nor practice given instead Kuga broke the shackles that have bound us for ages, breaking the chain of ignorance and shredding the veil of illusion or Maya, awakening us from the sleep of ages. Henceforth it was no more a matter of our effort in scaling and climbing but the divine lifting us. We just needed to sit in silence and all else shall take place.
Having hibernated for ages, the Guru has come to awaken us and lead us to the next level. Let us take his hand and invite him into our hearts. We have come to do his work but have forgotten our purpose and deviated. He has come to remind us. Time and again the guru drops by to remind us of the promise or obligation towards the divine. The divine asks of us to admit him into our hearts so that he could do his work through us. As Sri Ramakrishna explains, "When the mind learns to dwell there (at the heart chakra), man experiences his first spiritual awakening", the veil of illusion that had us believe that we were separate is pulled aside and Reality, our real self, is shown.
Hence we cannot possibly try to understand these states merely by reading about them but need to experience it. We have to empty the Self of all previous learning first before coming to experience the truth that dwells and shines in the innermost cave of the heart. With the knowledge and experience gained from external means as we enter the inner corridors of the heart, we come to drop each, negating them as false till what prevails is only the truth. To find the Self in the cave is to find Kuga (Lord Muruga).
Hence we cannot possibly try to understand these states merely by reading about them but need to experience it. We have to empty the Self of all previous learning first before coming to experience the truth that dwells and shines in the innermost cave of the heart. With the knowledge and experience gained from external means as we enter the inner corridors of the heart, we come to drop each, negating them as false till what prevails is only the truth. To find the Self in the cave is to find Kuga (Lord Muruga).