Smouldering with rage, at heart depressed (5)
I believe the answer is:
aglow
'smouldering' is the definition.
(both can mean burning)
'with rage at heart depressed' is the wordplay.
'with' is a charade indicator (letters next to each other).
'at heart' says to take the centre.
'depressed' becomes 'low' (synonyms).
The middle of 'rage' is 'ag'.
'ag' next to 'low' is 'AGLOW'.
(Other definitions for aglow that I've seen before include "Smouldering" , "Warm - shiny" , "Gently radiant" , "Illuminated" , "Giving out a steady light" .)