Crossword Genius

Centre of circulation (5)

Ross

I believe the answer is:

heart

I'm a little stuck... Click here to teach me more about this clue!

This clue could be a double definition.

'centre' is the first definition.
(I know that centre can be written as heart)

'circulation' is the second definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.

'of' is the link.

Can you help me to learn more?

(Other definitions for heart that I've seen before include "Centre; valour" , "Player for Scottish team" , "It's in the chest" , "Centre; core" , "Spirit - core" .)

I've seen this clue in the Evening Standard.
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