Film company boss with lion's heart (6)
I believe the answer is:
studio
'film company' is the definition.
(as in a film studio)
'boss with lion's heart' is the wordplay.
'boss' becomes 'stud' (both can mean a metal decoration).
'with' means one lot of letters go next to another.
'heart' means to look at the middle letters.
The central letters of 'lion' are 'io'.
'stud'+'io'='STUDIO'
(Other definitions for studio that I've seen before include "MGM, for example" , "Atelier, say?" , "Artist's workroom - film company" , "Small apartment" , "Here one may record" .)