It basically just means close again here with a sense of the heart being healed. and a feeling of contentment "with much sweetness and contentment.”

The suggestion is to finish the period of contemplation /meditation by "liftng up the heart" which basically means opening the heart and trusting in God while singing His praises

So when the period of contmplation is over, the heart closes again with a feeling of being healed

https://blogs.oxford.anglican.org/lift-up-your-hearts/

"...The idea of the heart is a big idea. In contemporary culture, the heart is the seat of the emotions and especially the place of romantic love. In the Bible it is much more. The heart is the very centre of our inner life, our spiritual life, our emotions, our character and our will. The heart is the whole of who we are and how we are.[...]
What is that we are lifting up? When I ask a congregation to lift up their hearts, I’m asking you to lift your very selves to God
To lift up your heart is an act of trust in God even in the midst of all that is happening, even despite the grief and the things you cannot understand. To hold up your heart to God’s love in confidence that it will be held and healed and not rejected..."
https://blogs.oxford.anglican.org/lift-up-your-hearts/

note that one meaning of the phrasal verb "close up" means a wound closing, becoming sealed and healing

--------------------------------------------------
Note added at 2 hrs (2021-05-14 12:50:49 GMT)
--------------------------------------------------

https://www.collinsdictionary.com/dictionary/english/close-u...

--------------------------------------------------
Note added at 2 hrs (2021-05-14 12:52:26 GMT)
--------------------------------------------------

I hope the above links help your understanding of what the "heart" is representing