Assist some simple-hearted characters ascending (4)
I believe the answer is:
help
'assist' is the definition.
('help' can be a synonym of 'assist')
'some simple-hearted characters ascending' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'ascending' says the letters should be written backwards.
'pleh' can be found hidden inside 'simple hearted characters'.
'pleh' back-to-front is 'HELP'.
(Other definitions for help that I've seen before include "Beatles single" , "Hit from Band" , "Come to the aid of" , "Guide" , "one by the Beatles" .)