The western gate is the Apâna (down-breathing), that is speech, that is Agni (fire). Let a man meditate on that as glory of countenance and health. He who knows this, becomes glorious and healthy.

In plain words: The western door of the heart is the downward breath, linked to speech and to Agni, the god of fire. Whoever meditates on it this way gains a glowing face and good health.