They conquer lady's heart in stylish short poem (8)
I believe the answer is:
invaders
'they conquer' is the definition.
(people who invade or conquer)
'lady's heart in stylish short poem' is the wordplay.
'heart' indicates the central letters.
'in' means one lot of letters goes inside another.
'stylish' becomes 'in'.
'short' means to remove the last letter.
'poem' becomes 'verse' (verse is a kind of poem).
The middle of 'lady' is 'ad'.
'verse' with its last letter removed is 'vers'.
'in'+'vers'='invers'
'ad' going into 'invers' is 'INVADERS'.
(Other definitions for invaders that I've seen before include "They enter by force in order to conquer" , "Intruders, conquerers" , "Intruding army" , "Attackers entering another country" , "Plunderers" .)