Monster’s heart in circulation, getting on nerves (7)

I believe the answer is:

bunyips

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'nerves' is the definition.
I know nothing about this answer so I can't tell whether this works.

'monster's heart in circulation getting on' is the wordplay.
'monster' becomes 'bunyip' (I've seen this before).
'heart in circulation getting' becomes 's' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'on' is a charade indicator (letters next to each other).
'bunyip'+'s'='BUNYIPS'

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I've seen this clue in the Sydney Morning Herald.

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