The last stronghold of Subjectivity
The heart is the last stronghold of subjectivity. When the Citta sees the luminous cloud and penetrates it with the three characteristics, it is left with just that Knowing and enjoys that state for some time. Latter, when it returns to this, it is able to know that state and the Knowing of it. It is no longer located in the heart. It no longer has a physical location.
But the full freedom of the heart is still some way off. Only when Samaadhi has been fully cultivated will the Citta have the ability to rest in the Knowing at will: or alternatively stay with the Knowing of any arising perception, or phenomena, for as long as needed without any disturbance by it at all.