Pertaining to the heart (7)
I believe the answer is:
cardiac
'pertaining to the heart' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for cardiac that I've seen before include "Physiologically, of the heart" , "Relating to the heart" , "Sort of surgery" , "Relating to 8 down, part one" , "of hearts" .)