What does the cryptic crossword clue "After contraction, breathe artificially, deep down (2,5)" mean?

The definition is "down". The wordplay uses a hidden word. hidden in "breATHE ARTificially," The answer is AT HEART.

After contraction, breathe artificially, deep down (2,5)

Times Cryptic #28757 | 4 Across | 2023-11-10 flower