Cardiac specialist is a card (3,2,6)
I believe the answer is:
ace of hearts
'card' is the definition.
(ace of hearts is a kind of card)
'cardiac specialist is a' is the wordplay.
I cannot really understand how this works, but
'specialist' could be 'heart' (heart specialist is a kind of specialist) and 'heart' is found in the answer.
'a' is within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for ace of hearts that I've seen before include "red card?" , "Scottish team's top player" .)