Part of church losing hearts in void (6)
I believe the answer is:
cancel
'void' is the definition.
(I know this)
'part of church losing hearts' is the wordplay.
'part of church' becomes 'chancel' ('chancel' is part of 'church').
'losing' indicates named letters should be taken away.
'hearts' becomes 'h' (abbreviation used in card games e.g. bridge).
'chancel' with 'h' taken out is 'CANCEL'.
'in' is the link.
(Other definitions for cancel that I've seen before include "Cross out or annul" , "Call off or invalidate" , "Call off (arranged event)" , "Annul, revoke" , "Scrub" .)