The most common and most likely answer to this crossword clue is the 10 letter word TRANSPLANT
I've seen this crossword clue in The Daily Telegraph
T
R
A
N
S
P
L
A
N
T
Buddy explains!

The straight part
We know that "Change of heart" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case change of heart = transplant.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does TRANSPLANT mean?
TRANSPLANT noun- An act of uprooting and moving (something).
- Anything that is transplanted.
- An operation in which tissue or an organ is transplanted.
- A transplanted organ or tissue.
- Someone who is not native to their area of residence.
- To uproot (a growing plant), and plant it in another place.
- To remove (something) and establish its residence in another place; to resettle or relocate.
- To transfer (tissue or an organ) from one body to another, or from one part of a body to another.