B.G 8.12 and 13
सर्वद्वाराणि संयम्य मनो हृदि निरुध्य च। मूर्ध्न्याधायाऽत्मनः प्राणमास्थितो योगधारणाम् ॥१२॥
sarvadvārāṇi saṁyamya mano hr̥di nirudhya ca। mūrdhnyādhāyā'tmanaḥ prāṇamāsthito yogadhāraṇām ॥12॥
Having restrained all the gates, fixing the mind in the lord Nārāyaṇa, placing the breath in the head, one remains established in the practice of yoga.
ओमित्येकाक्षरं ब्रह्म व्याहरन् मामनुस्मरन्। यः प्रयाति त्यजन् देहं स याति परमां गतिम् ॥१३॥
omityekākṣaraṁ brahma vyāharan māmanusmaran। yaḥ prayāti tyajan dehaṁ sa yāti paramāṁ gatim ॥13॥
Whoever, uttering the one-syllabled Om, which is Brahman, and remembering Me, departs leaving the body, attains the supreme destination.
Gīta Bhāshya 8.12 and 13
It is not possible to have the mind in the heart and to place the breath in the head. Wherever lies the vital breath, the supreme Prāṇa, there lies the mind, and the living being. So the word 'hṛdi' in the current context means lord Nārāyaṇa. A testimonial is given to substantiate the same - "Because you take away the world, you are indeed called 'hṛdi'". 'yogadhāraṇām' means being engrossed in Yoga alone.
If one departs through any other passage without the Brahman-nāḍī, then, without attaining liberation, one reaches another state of existence. Therefore one should restrain all other openings.
"Departing (from the body) through the eye one reaches the Sun, and through the hearing the directions."
- it is stated thus in the Vyāsa-yoga. Same is stated in the Mokṣa-dharma (section of the Mahabharata) as well.
The phrase 'In the heart' means in lord Nārāyaṇa.
"Because you take away the world, you are indeed called 'hṛdi'."
- stated thus in the Padma Purāṇa.
Indeed, when the vital breath is situated in the head, the stability of the mind in the heart is not possible:
"Wherever lies the vital breath, the supreme Prāṇa, there lies the mind, and the living being."
- stated thus in Vyāsayoga.
The word 'yogadhāraṇā' means being engrossed in yoga alone — this is the intended meaning.
Gīta Tātparya 8.12 and 13
'ekākṣaram' - the Supreme Brahman.
Since the Supreme Brahman is conveyed by the single syllable (Oṁ), he is called 'ekākṣaram', i.e. single syllable.
