Heaven exists in exhibit (8)
I believe the answer is:
paradise
'heaven' is the definition.
(synonyms)
'exists in exhibit' is the wordplay.
'exists' becomes 'is' ('be' can be a synonym of 'exist').
'in' means one lot of letters goes inside another.
'exhibit' becomes 'parade' (synonyms).
'is' inserted inside 'parade' is 'PARADISE'.
(Other definitions for paradise that I've seen before include "Elysian fields" , "Utopia" , "Idyllic place" , "Persian word which in Hebrew became 'a blessed place'" , "What was lost to the poet" .)