At heart of row carrying on without a break (6)
I believe the answer is:
legato
'without a break' is the definition.
I can't tell whether this defines the answer.
'at heart of row carrying on' is the wordplay.
I cannot really understand how this works, but
'at' is within the answer.
'of' could be 'o' and 'o' is found in the answer.
'on' could be 'leg' (cricket term, fielding positions) and 'leg' is located in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for legato that I've seen before include "In music, the opposite of staccato" , "Got ale (anag.)" , "scored smoothly" , "Don't play roughly" , "with smooth execution" .)