The most common and most likely answer to this crossword clue is the 8 letter word ASYSTOLE
I've seen this crossword clue in The Guardian
A
S
Y
S
T
O
L
E
Buddy explains!
The straight part
We know that "It’s bad for circulation" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case it’s bad for circulation = asystole.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does ASYSTOLE mean?
ASYSTOLE noun- Absence of systole; failure of the heart to contract.