I think it is metaphorical myself. This is probably similar to the verses that talk about "thinking from the heart".
No..no..nope there are more than 100 verses in Quran that uses the word "Heart/hearts"
, and many of them do use that word metaphorically. But This verse from chapter 33 is different
"Allah has not made for a man two hearts in his interior"
"Allah has not made your wives whom you declare unlawful your mothers"
"Allah has not made your adopted sons your true sons."
They are not metaphorical statements., Off course here Allah made that verse for Prophet PBUH marrying and sleeping with that Zaynab., because she was not the wife of his real son but adoptes son's wife...