The most common and most likely answer to this crossword clue is the 10 letter word HEARTSEASE
I've seen this crossword clue in The Guardian
H
E
A
R
T
S
E
A
S
E
More clues leading to the result HEARTSEASE
Buddy explains!

The straight part
We know that "Peace of mind/Peace of mind" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case peace of mind/peace of mind = heartsease.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 HEARTSEASE mean?
HEARTSEASE noun- A common European wild flower, Viola tricolor; the wild pansy.