In the heart resides this Ātman. Here there are one hundred and one nāḍīs. Each of them has one hundred branches. Each branch has seventy-two thousand ramifications. In them circulates vyāna.

This verse describes the architecture of the subtle body: the system of nāḍīs that emanates from the spiritual heart.

Hṛdi hy eṣa ātmā — in the heart resides the Ātman. The hṛdaya is not just the physical organ but the spiritual center, the “cave of the heart” (hṛdaya-guhā) mentioned in other Upaniṣads. It is the point where the individual Self connects with the universal Self.

Ekaśataṃ nāḍīnām — one hundred and one nāḍīs. The nāḍīs are subtle channels through which prāṇa flows. The number 101 also appears in the Kaṭha Upaniṣad. One of them — the suṣumnā — leads upward, toward liberation.

Śataṃ śatam ekaikasyāḥ — each has one hundred branches. The network ramifies: 101 × 100 = 10,100 secondary channels.

Dvāsaptatiḥ pratiśākhānāḍīsahasrāṇi — seventy-two thousand ramifications per branch. The complete mathematics: 101 × 100 × 72,000 = 727,200,000 channels in total. The symbolic number 72,000 appears frequently in haṭha-yoga texts.

Āsu vyānaś carati — in them circulates vyāna. While prāṇa receives, apāna eliminates and samāna distributes in the center, vyāna is the circulatory prāṇa. It travels throughout the body through this vast network of nāḍīs, carrying vital energy to every cell.

This subtle anatomy is the map of prāṇāyāma: the yogī learns to feel and direct the flow of vyāna through the nāḍīs, eventually concentrating it in suṣumnā to awaken the kuṇḍalinī.