Assuming legal responsibility, this person's heart may be true (6)
I believe the answer is:
surety
'assuming legal responsibility this person's heart' is the definition.
'surety' can be an answer for 'person's' (surety is a kind of person). I am not sure about the rest of the definition.
'be true' is the wordplay.
I cannot really see how this works, but
an anagram of 'true' is 'uret' which is present in the answer.
This may be the basis of the clue (or it may be nonsense).
'may' is the link.
Can you help me to learn more?
(Other definitions for surety that I've seen before include "Money given as guarantee of action" , "Safeguard; certainty" , "Legal safeguard against loss" , "Safeguard given against financial loss" , "Warranty, guarantee" .)