Bank is genuinely heartless (4)
I believe the answer is:
rely
'bank' is the definition.
(to bank on something is to rely on it)
'genuinely heartless' is the wordplay.
'genuinely' becomes 'really' (I've seen this before).
'heartless' means to remove the middle letters.
'really' with its centre removed is 'RELY'.
'is' acts as a link.
(Other definitions for rely that I've seen before include "Depend, bank" , "Depend or lean on" , "Old rally" , "Bank (on someone)" , "Trust, depend" .)