Percentage losing heart during speech surgery (9)
I believe the answer is:
operation
'surgery' is the definition.
('operation' can be a synonym of 'surgery')
'percentage losing heart during speech' is the wordplay.
'percentage' becomes 'piece' (piece is a kind of percentage).
'losing heart' says to hollow out the word (remove centre letters).
'during' means one lot of letters goes inside another.
'speech' becomes 'oration' (oration is a kind of speech).
'piece' with its centre taken out is 'pe'.
'pe' going within 'oration' is 'OPERATION'.
(Other definitions for operation that I've seen before include "activity" , "running" , "financial transaction" , "management" , "Surgical or military procedure" .)