Internal contraction due to extremely speedy boa? (7)

I believe the answer is:

systole

'internal contraction' is the definition.

'extremely speedy boa?' is the wordplay.
'extremely' suggests removing the centre.
'boa?' becomes 'stole' (both can mean a scarf or shawl).
'speedy' with its middle taken out is 'sy'.
'sy'+'stole'='SYSTOLE'

'due to' is the link.

I've seen this clue in The Times.

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