piṇḍe vāyv-agni-saḿśuddhe
hṛt-padma-sthāḿ parāḿ mama
aṇvīḿ jīva-kalāḿ dhyāyen
nādānte siddha-bhāvitām
pinde -- within the body; vayu -- by air; agni -- and by fire; samsuddhe -- which has become completely purified; hrit -- of the heart; padma -- upon the lotus; stham -- situated; param -- the transcendental form; mama -- of Mine; anvim -- very subtle; jiva-kalam -- the Personality of Godhead, from whom all living entities expand; dhyayet -- he should meditate upon; nada-ante -- at the end of the vibration of om; siddha -- by perfected sages; bhavitam -- experienced.
According to Srila Sridhara Svami, the pranava, or omkara, has five parts: A, U, M, the nasal bindu and the reverberation (nada). Liberated souls meditate upon the Lord at the end of that reverberation.