At heart, many need to help out (4)
I believe the answer is:
amid
'at heart' is the definition.
I know nothing about this answer so I cannot tell whether this works.
'many need to help out' is the wordplay.
I cannot really understand how this works, but
'many' could be 'm' (Roman numeral for a thousand) and 'm' is found in the answer.
'help' could be 'aid' (synonyms) and 'aid' is located in the remaining letters.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for amid that I've seen before include "A dim sort of preposition" , "Among" , "In the course of" , "Surrounded by" , "In the thick of" .)