Left off radical treatment caught affecting the heart (7)
I believe the answer is:
cardiac
'affecting the heart' is the definition.
(cardiac means relating to the heart)
'left off radical treatment caught' is the wordplay.
I cannot really see how this works, but
'radical' could be 'r' (chemistry abbreviation) and 'r' is found within the answer.
'caught' could be 'ca' (I've seen this in other clues) and 'ca' is found in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for cardiac that I've seen before include "of hearts" , "Of the heat, perhaps illness" , "Relating to 8 down, part one" , "Sort of surgery" , "one with a heart disorder" .)