Label not showing initial heart (6)
I believe the answer is:
ticker
'heart' is the definition.
(informal term for the heart)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for ticker that I've seen before include "Telegraph instrument" , "Maybe watch" , "Slang heart or old spring watch" , "Old watch or informal heart" , "Old clock or slang heart (6)" .)