The hearts, for instance, one grills (5)
I believe the answer is:
pumps
'the hearts' is the definition.
('pump' can be a synonym of 'heart')
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for pumps that I've seen before include "causes of inflation?" , "leading questions" , "needed by cyclists" , "Mechanical devices that move fluid or gas" , "footwear" .)