Perhaps the heart is her majesty's manager (9)
I believe the answer is:
organiser
'manager' is the definition.
(I've seen this before)
'perhaps the heart is her majesty's' is the wordplay.
I cannot quite understand how this works, but
'heart' could be 'organ' (I've seen this in another clue) and 'organ' is present in the answer.
'is' is found in the answer.
'her majesty' could be 'er' (Elizabeth Regina) and 'er' is found in the answer.
This accounts for all the letters.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for organiser that I've seen before include "Co-ordinator" , "Runner" , "arranger" , "impresario" , "One making arrangements" .)