Hridaya is the Sanskrit word for spiritual heart coming from ‘hrid’ (centre) and ‘ayam’ (this). It is said to be different from the physical heart that regulates blood circulation and gives the body life.
Heart (hridaya) is the deepest consciousness, the center of reality, the light of consciousness in which the entire universe is rooted. Because the whole is contained in every part, this heart centre pervades the entire universe and our body. The universe beats like a cosmic heart. The pulsation is on the macrocosmic level, in which it unfolds our universe, holds it in place and then withdraws it after many millions of years; and on the microcosmic level in which the same pulsation takes place in every nanosecond with the creation of every thought and the beating of the human heart. In meditation this profound vibratory movement can be contacted in the stillness.
The eternal pulsation-vibration (spanda) of Shiva’s heart drives the entire process of manifestation and dissolution.
– Paul Muller-Ortega
Paul Muller-Ortega says that according to Abhinavagupta, the Heart in Kashmir Shaivism is the very Self of Shiva and the Goddess (Devi), who is not different from Shiva. This entire universe (external) is the heart of Devi, while the heart of Shiva is contained within our own body (internal). The Hridaya Heart is the abode of their union, and pure consciousness as well as unlimited bliss.
When we steady our breath we feel the steadying of our thoughts. Then the thoughts turn inward and melt away at a point. Watching this point, where the thoughts vanish, will also help us to merge ourselves in the Hridaya.
– V. Ganesan