Legendary spinner's general aches isolated in the heart (8)

I believe the answer is:

lachesis

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'the heart' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.

'legendary spinner's general aches isolated' is the wordplay.
'LACHESIS' is hidden in amongst the letters.
However, I'm not sure how this is indicated.

'in' is the link.

Can you help me to learn more?

(Other definitions for lachesis that I've seen before include "One of the three Fates in Greek myth" , "Fate" .)

I've seen this clue in The Guardian.

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