Stunner -- she loses heart, being pinched by sailor (5)
I believe the answer is:
taser
'stunner' is the definition.
(I've seen this before)
'she loses heart being pinched by sailor' is the wordplay.
'loses heart' suggests removing the centre.
'being pinched by' indicates putting letters inside (inserted letters get pinched or taken).
'sailor' becomes 'tar' (slang term for a sailor).
'she' with its centre removed is 'se'.
'se' inserted within 'tar' is 'TASER'.
(Other definitions for taser that I've seen before include "Paralysing device used by police" , "Stunning device" , "Shocking device used by the police?" , "Police stun weapon" , "PC kit" .)