Depend on keeping a brave heart in a race (5)
I believe the answer is:
relay
'a race' is the definition.
(thesaurus)
'depend on keeping a brave heart' is the wordplay.
'depend on' becomes 'rely' (I've seen this before).
'keeping' means one lot of letters goes inside another.
'heart' says to take the centre.
The middle letter of 'brave' is 'a'.
'rely' placed around 'a' is 'RELAY'.
'in' acts as a link.
(Other definitions for relay that I've seen before include "track event" , "Team of workers" , "Pass on - put down again" , "Receive and pass on - race" , "Hand, pass on" .)