'That Self abides in the heart. And this is the etymological explanation. The heart is called hridayam, instead of hrzdy-ayam, i. e. He who is in the heart. He who knows this, that He is in the heart, goes day by day (when in sushupti, deep sleep) into heaven (svarga), i.e. into the Brahman of the heart.

In plain words: The Self lives in the heart. Even the Sanskrit word for heart, hridayam, is explained as meaning 'He is in the heart.' A person who knows this goes into Brahman, a kind of heaven, each night in deep sleep.