Discover nature changes hearts (7)
I believe the answer is:
unearth
'discover' is the definition.
(thesaurus)
'nature changes hearts' is the wordplay.
'changes' indicates an anagram.
'hearts' becomes 'h' (abbreviation used in card games e.g. bridge).
'nature' anagrammed gives 'uneart'.
'uneart'+'h'='UNEARTH'
(Other definitions for unearth that I've seen before include "Bring out of obscurity" , "Disclose" , "reveal" , "Track down" , "Cut a certain wire" .)