To me, a good-hearted ass! (4)
I believe the answer is:
moke
'ass' is the definition.
(moke is a kind of ass)
'to me a good-hearted' is the wordplay.
I cannot really understand how this works, but
'good' could be 'ok' and 'ok' is present in the answer.
'me' is found in the answer.
No letters remain.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for moke that I've seen before include "cross" , "Beast of burden" , "Mule" , "Donkey (slang)" .)