Ancient city bringing heart of Paris into play (4)
I believe the answer is:
troy
'ancient city' is the definition.
(I've seen this before)
'heart of paris into play' is the wordplay.
'heart of' says to take the centre.
'into' indicates putting letters inside.
'play' becomes 'toy' ('toy' can be a synonym of 'play').
The centre of 'paris' is 'r'.
'r' put inside 'toy' is 'TROY'.
'bringing' is the link.
(Other definitions for troy that I've seen before include "Ancient city besieged by the Greeks" , "Helen of --, beauty" , "Besieged city which fell to Wooden Horse" , "See 7" , "System of weights introduced by French" .)