Writing in favour of someone with no heart (5)
I believe the answer is:
prose
'writing' is the definition.
(I've seen this in other clues)
'in favour of someone with no heart' is the wordplay.
'in favour of' becomes 'pro' (I've seen this before).
'with no heart' suggests removing the centre.
'someone' with its middle taken out is 'se'.
'pro'+'se'='PROSE'
(Other definitions for prose that I've seen before include "Not poetry" , "Text" , "Literary genre" , "Normal written language" , "Ordinary spoken or written language" .)