Burly but showing a very soft heart in a row (9)
I believe the answer is:
strapping
'burly' is the definition.
(I know that burly can be written as strapping)
'a very soft heart in a row' is the wordplay.
'a very soft heart' becomes 'app' (I can't explain this - if you can you should believe this answer much more).
'in' is an insertion indicator.
'a row' becomes 'string' (I've seen this before).
'app' inserted within 'string' is 'STRAPPING'.
'but showing' is the link.
Can you help me to learn more?
(Other definitions for strapping that I've seen before include "Big" , "Tying up" , "Robust" , "Burly" , "Brawny" .)