Composer crossing heart on island (7)
I believe the answer is:
rossini
'composer' is the definition.
(Italian composer Gioachino Rossini)
'crossing heart on island' is the wordplay.
'heart' means to look at the middle letters.
'on' is a charade indicator (letters next to each other).
'island' becomes 'i'.
The centre of 'crossing' is 'rossin'.
'rossin'+'i'='ROSSINI'
(Other definitions for rossini that I've seen before include "Composer born 29 Feb 1792" , "He composed operas" , "Staff writer" , "Composer of the opera William Tell, d. 1868" , "Italian scorer" .)