Greedy — backing stratagem, that is — not heartless (8)
I believe the answer is:
esurient
'greedy' is the definition.
('esurient' can be a synonym of 'greedy')
'backing stratagem that is not heartless' is the wordplay.
'backing' says the letters should be written backwards.
'stratagem' becomes 'ruse' (I've seen this before).
'that is' becomes 'ie' ('i.e.' can be a synonym of 'that is').
'heartless' means to remove the middle letters.
'not' with its centre removed is 'nt'.
'ruse' in reverse letter order is 'esur'.
'esur'+'ie'+'nt'='ESURIENT'
(Other definitions for esurient that I've seen before include "Hungry, greedy" , "Greedy; ensure it (anag.)" , "could eat a horse" , "Rapacious" , "Hungry; retinues (anag.)" .)