In turn, doctor very brave just opening heart (5)
I believe the answer is:
bosom
'heart' is the definition.
(bosom can figuratively mean the heart)
'in turn doctor very brave just opening' is the wordplay.
'in turn' is a reversal indicator (letters turning around).
'doctor' becomes 'mo' (medical officer).
'very brave just opening' becomes 'sob' (I can't justify this - if you can you should believe this answer much more).
'mo'+'sob'='mosob'
'mosob' backwards is 'BOSOM'.
(Other definitions for bosom that I've seen before include "Chest; very close (friend)" , "Woman's chest" , "Intimate" , "Woman's breast" , "(Female's) chest" .)