He gets new heart from a girl (7)
I believe the answer is:
heather
'a girl' is the definition.
'he gets new heart' is the wordplay.
'gets' means one lot of letters go next to another.
'new' indicates anagramming the letters.
'heart' is an anagram of 'ather'.
'he'+'ather'='HEATHER'
'from' acts as a link.
(Other definitions for heather that I've seen before include "that grows up in the Highlands" , "Moorland shrub" , "Girl's name - ling" , "Moorland plant" , "Ericaceous shrub" .)