Heroes' disheartening loss after vow (5)
I believe the answer is:
idols
'heroes'' is the definition.
(I've seen this before)
'disheartening loss after vow' is the wordplay.
'disheartening' suggests removing the centre.
'after' means one lot of letters go next to another.
'vow' becomes 'I do' (I do, marriage vow).
'loss' with its centre taken out is 'ls'.
'ls' after 'ido' is 'IDOLS'.
(Other definitions for idols that I've seen before include "Solid kind of images" , "Graven images sometimes worshipped" , "objects such as the Golden Calf" , "Effigies worshipped as gods" , "Solid (anag.)" .)