Heart shown by popular bank (6)
I believe the answer is:
inside
'heart' is the definition.
(thesaurus)
'by popular bank' is the wordplay.
'by' is a charade indicator (letters next to each other).
'popular' becomes 'in' ('in' can mean trendy).
'bank' becomes 'side' (synonyms).
'in' next to 'side' is 'INSIDE'.
'shown' is the link.
(Other definitions for inside that I've seen before include "Enid is (anag) - within" , "Not external, perhaps in prison" , "locked up" , "being held" , "Stomach etc - in prison?" .)