This Center in the Heart is that point within the body through which the Infinite Being animates the body with the light of consciousness and the sense of being, as "I." Where the chakras can be compared to prism-like lenses of a movie projector providing interpretation of gross, subtle and spiritual images, the Heart Center is the pure light, like a self-effulgent screen, in that projector that gives the sense of identity and reality to the projected images appearing on its surface. The Hrdayam / One Star is located in the heart itself. The physical heart is 7/8 to the left of the sternum and 1/8th to the right. In that 1/8th portion is located the pacemaker or synod of the heart, which give the pulse or beat to the heart. It is the place where we point when we say "I." In Ayurvedic medicine it is mentioned as the seat of consciousness.
In the Katha Upanishad (and others), it is said to be that place from which all the nerves of the body have their origin, as well as a major nerve (the right Vegas nerve), which rind from this location to the crown center (the Sahasrara or thousand pedaled lotus).
It is not the same as the anahata chakra, which is the nexus of nerves and related glands and organs located directly behind the sternum, between the bottom of the sternum and nape of the neck.
The awakening of this Heart Center is the purpose of all religious teachings and the focus of all religious experience, where that experience relates purely to the spiritual, i.e., the purpose of yoga - to isolate the "seer" - the subject "I" through the relinquishment / dissolving of the limited idea that our identity is bound to sensations of the body and the tyranny of thoughts, impressions and images in the mind.
In the Bible: Ecclesiastics: 10:3, is stated "The wise man's heart inclines him to the right, the fool's to the left" In the New Testament, Christ says: "The Pure in heart shall see God ("I AM THAT I AM)".
The Hrdayam is called the One Star (Ik Tar), because it has a pulling force, like gravity, that sucks in and dissolves all thoughts and images from the mind, while at the same time, like the sun, It radiates living light that outshines all images. "Hrd" means literally "That which sucks in everything" and "ayam" - "This" and "Expansion" - together meaning the core of ones being or "Heart."
The Heart is the place out of which everything expands and is withdrawn. In terms of the realized experience, it is similar to a concept of a Black Hole, wherein one experiences the pulsing incandescent radiance of Being in the atma nadi between the Hrdayam (Heart) and Sahasrara (Crown), while attention is disengaged, so that no objects can be seen in association to the pulsing pervasive sense of "I" – felt as a radical force one might call spaghettification, as physicists describe the dissolution of particles and atoms being sucked into a Black Hole. Nothing remains, not time nor space.
In the Yoga Sutras of Patanjali there are 2 areas recommended to focus ones awareness in meditation. One of these is the crown center and the other, the self-effulgent light in the heart. While some mistakenly assume that heart means the anahata chakra, in fact, only the Hrdayam is self-effulgent. All other centers have their light from this one center, similar to the light in a movie projector (the Self), that animates (lights) the images through the lenses (chakras) onto the screen (of consciousness).
The Hrdayam is called the Solar Orb, because it is the source of being and consciousness (gravitation and light), and the Sahasrara is called the Lunar Orb, because it is the reflected consciousness in which the dimensions of the gross, subtle and spiritual universe appears.
When the sun in the heart awakens, the experience is like coming out of a stupor or amnesia. The sense of "I" - the seer, abides in Itself without attachment, clinging or attention to objects. Even attention to silence, stillness or a blank is relinquished, along with the identity to the sensations of the body and images, impressions and thoughts of the mind.
You experience a sense of single pervasiveness, timelessness, and unconditioned, uncaused being. "Nothing is separate and you cling to nothing. Everything is empty, clear, self- illuminating..." (from the 3rd Zen Patriarch: Faith Mind")
The 2 poles of the heart (Hrdayam) and Crown (Sahasrara) blaze with light, and the nerve between (called atma, amrita or para nadi) radiates incandescently, vibrating with unstruck soundless sound. Simultaneously, you may see a flame, sometimes multi-colored, rising through the spine and the crown of the head. In Kundalini Yoga, the Mind Nerve. In Physiology, the Vagus Nerve that runs from the Spiritual Heart to the Crown.
Yoga is the union of the individual unit of consciousness with the all-pervasive universal consciousness - the infinite being. But this union is not of 2 separate things that have to be united, as the ever present Reality and Truth is that the infinite being lights each of us born in the world in the heart as the Light of our light, the "I" of our "i."
As the mind begins to become electromagnetically still and balanced, there is an automatic inversion of the mind from outgoing reflecting images, to pure reflection of the Heart. We call this the discriminate facility (budhi), but it is the pulling force of the Heart that turns the mind inward.
There is nothing outside of the Self, and when the mind reflects the Self in the Heart, there is a "hearing" - recognition (sravana/sunia), "remembrance" (manna) and "abiding" (niddidyasana) that resonates in a manner that attunes all the nerves of the body to the Heart, resulting in awareness of one's Self as undifferentiated consciousness, where "inside - outside" simply dissolve and vanish like a mirage, "...everything is whole." (Yogi Bhajan)
The PDF file: What is the One Star?