Talking of setter's wheezing heartlessly creates an pleasant atmosphere (6)

I believe the answer is:

miasma

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'atmosphere' is the definition.
(I know that miasma is a type of atmosphere)

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for miasma that I've seen before include "Foul vapour" , "Unwholesome or foreboding atmosphere" , "Foul vapours or unwholesome air" , "Unpleasant smell/vapour" , "Unpleasant vapour or influence" .)

I've seen this clue in The Guardian.

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