Guy giving a failure fresh heart (4)
I believe the answer is:
dude
'guy' is the definition.
(both can informally mean a man)
'giving a failure fresh heart' is the wordplay.
'giving' means one lot of letters go next to another.
'a failure' becomes 'dud' (dud is a kind of failure).
'heart' means to look at the middle letters.
The centre of 'fresh' is 'e'.
'dud'+'e' is 'DUDE'.
(Other definitions for dude that I've seen before include "Stylish chap" , "US geezer" , "Stylish man (US)" , "Man (US colloq.)" , "An American dandy out west" .)