Pressing the sīvanī nāḍī with the right ankle, and always with the left heel [on the perineum], this is known as Siddhāsana.

This verse adds technical precision by mentioning the sīvanī-nāḍī, the energy channel that runs along the perineum. This nāḍī is the subtle counterpart of the perineal raphe, the tissue line marking the embryonic fusion.

The pressure on sīvanī-nāḍī has a profound effect on the flow of prāṇa. According to tantric texts, this nāḍī connects directly with Suṣumnā, and its stimulation can awaken the dormant kuṇḍalinī.

Nityam — “always” or “constantly” — reiterates that Siddhāsana must be practiced regularly. Tradition holds that twelve years of continuous practice lead to perfection (siddhi).

The specification of the left heel below corresponds to standard practice, though some texts allow alternating legs to maintain muscular balance.