Heartlessly deny repulsive ruling family (7)
I believe the answer is:
dynasty
'ruling family' is the definition.
(as in a royal dynasty)
'heartlessly deny repulsive' is the wordplay.
'heartlessly' means to remove the middle letters.
'repulsive' becomes 'nasty' (I've seen this before).
'deny' with its middle removed is 'dy'.
'dy'+'nasty'='DYNASTY'
(Other definitions for dynasty that I've seen before include "Powerful family line" , "Song perhaps" , "Succession of relatives" , "Sequence of powerful leaders in the same family" , "TV series" .)