Maybe the opposite of one crossing heart (6)
I believe the answer is:
ticker
'heart' is the definition.
(informal term for the heart)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for ticker that I've seen before include "Slang heart or old spring watch" , "Heart (sl.)" , "Maybe watch" , "- - -tape machine" , "timer" .)