What does the cryptic crossword clue "Candour shown by this type of operation (4,5)" mean?

The wordplay uses a charade (building blocks). OPEN (synonym="OPEN") + HEART (synonym="HEART") = OPENHEART The answer is OPENHEART.

Candour shown by this type of operation (4,5)

Guardian Cryptic #29597 | 9 Across | 2025-01-21 flower