Musician in state of nervousness, losing heart (6)
I believe the answer is:
fluter
'musician' is the definition.
(I know that fluter is a type of musician)
'state of nervousness losing heart' is the wordplay.
'state of nervousness' becomes 'flutter' (someone in a flutter is nervous).
'losing heart' says to hollow out the word (remove centre letters).
'flutter' with its middle removed is 'FLUTER'.
'in' acts as a link.
(Other definitions for fluter that I've seen before include "Instrumentalist" , "piper" , "` ` Phil the ...'s ball ' ' (song)" .)