Veteran soldier's heart (5)
I believe the answer is:
oldie
'veteran' is the definition.
(I've seen this before)
'soldier's heart' is the wordplay.
'heart' says to take the centre.
The centre of 'soldier' is 'OLDIE'.
(Other definitions for oldie that I've seen before include "Venerable person/thing" , "classic film perhaps" , "Perennially popular song or film, often golden" , "Once popular song (perhaps "golden")" , "Aged person or thing" .)