The Spiritual Heart is our essential and ultimate nature, the ineffable dimension of our being. It is another name for the Supreme Self, atman, the witness consciousness, as mentioned above.

The Ultimate Reality is transcendent and immanent in any aspect of the Macrocosm. It is the ultimate essence of all. It is a condition beyond duality. Through spiritual maturity, the Heart is revealed as something more than an individual dimension of our being, after which it ceases to be expressed in terms of duality. It represents the whole in which Subject and object, the witness and witnessed, are one. Seen as consciousness, the Heart is unlimited.

It is the infinite Light. It is also the absolute freedom and spontaneity of this Light of consciousness, which appears to us in different forms in manifestation.

The Heart as the Supreme Consciousness is like the ocean, which is reflected both as the vastness of sea and the different shapes of its waves. Similarly, the awareness of the Spiritual Heart is a complete path in itself. It can lead to a direct knowledge integrating all the energies, the whole of manifestation, but at the same time, it reveals the Ultimate Supreme Transcendence.

The heart is called Hridaya it is derived from the Sanskrit word Hridayam (hrit + ayam), which simply means “this is the center”. This is not our physical; it is Spiritual. It is the Divine or Spiritual Center, which is essentially synonymous to various other terms such as Atman,  the cave of Intuitive Wisdom, the cave of Intuitive, the cave of Celestial Bliss,  the inner Home, the cave of Silence, the cave of deep Samadhi,  absolute void, natural state of inner Being, Tenth Gate, Chautha Pad or fourth state, Turiyaa Avastha, Tenth Gate (Dasam Duar), Conscious Principle, Eternal Essence, the city of Baygumpura or Brahmpura, Sachkhand, Truth, Light, the Kingdom of God, the Ultimate Resort of the Self of all, and so on.

Since the “cave of the Heart” is not the physiological cavity or hole in the heart, here it means only the core of the personality. It is the condition of the evolved Soul  which stands for Divine Virtues such as selflessness, egolessness, desirelessness, obedience, compassion, devotion, love, kindness, sympathy, selfless Seva, charity, bliss, peace, joy, tranquility, knowledge, Shabad-Surti or Naam consciousness, humility, contentment, forgiveness, nonviolence, unshakable faith, equanimity, self-discipline, righteousness, discriminating intellect, endurance, poise, patience, detachment, physical-control, truthfulness, mental control, purity, highest standard of moral and character, God-centered Karma or activities, seeing of One God in everything, living by God’s Hukam (Will), and so on. Thus the “cave of the Heart” is that arena in the human mind from where these noble urges flow out.

The “cave of the Heart” is the Seat Divine, where the All-pervading Omnipresent within (Source, Origin) can be contacted, in the very heart of the seeker. It is not an object, or a self-evident truth placarded before our eyes, or an immediate datum given to us within the range of our common experiences. As the scriptures tell us, It cannot be reached by mere instructions, material intelligence, learning, reading or scholarships. The Atman must be realized and its ultimate identity with Prmatam discovered the Unity of Atman and Paramatma as Unconditioned Consciousness.

Everything, including the physiological heart, is in Parmatam, the Substratum (Adhar) for the pluralistic phenomenal world of objects. The waves, the ripples, the foam, the lather all of them are the ocean. The bracelet, the necklace, the chain, the earrings, the nose-rings all of them are nothing but gold. Similarly, the one Spirit is within everything as oil is hidden in seeds, or as butter is hidden in milk, or as water is hidden beneath the earth, or as the fire is hidden in woods.

There are no two Truths such as one within our heart and one without us. The Divine Essence is one and the same within us as well as everywhere in the Cosmos. In that sense, It cannot be said to be either in or out.

The Spiritual Heart is not just the soul and the psychic activity

The Heart is considered the seat of feelings, of psychic activity. But this is just a relative and individual dimension of the Heart.
The world of individual emotions, the human soul, is to be overcome through detachment for revealing the true universal significance of the Heart. So, Atman, the Spiritual Heart, has no physical or mental dimensions as such and does not express itself other than as a mere transfiguring tremor. But as yogis say, unquestionably God exists and He alone is real.