Heir hit gold (9)
I believe the answer is:
successor
'heir' is the definition.
(I know that heir can be written as successor)
'hit gold' is the wordplay.
'hit' becomes 'success' (as in a hit song).
'gold' becomes 'or' ('or' is the heraldic name for gold).
'success'+'or'='SUCCESSOR'
(Other definitions for successor that I've seen before include "one coming after you" , "One taking over from another" , "One follows next in order" , "Follower (in post)" , "I follow" .)