Admirers flatter old Russians heartlessly (7)
I believe the answer is:
suitors
'admirers' is the definition.
(suitor is a kind of admirer)
'flatter old russians heartlessly' is the wordplay.
'flatter' becomes 'suit' (I've seen this in another clue).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'heartlessly' suggests removing the centre.
'russians' with its centre taken out is 'rs'.
'suit'+'o'+'rs'='SUITORS'
(Other definitions for suitors that I've seen before include "Beaux" , "They want wives" .)