The most common and most likely answer to this crossword clue is the 7 letter word INHALES
I
N
H
A
L
E
S
Buddy explains!
The straight part
We know that "Fills chest with" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fills chest with = inhales.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 INHALES mean?
INHALES noun- An inhalation.
- To draw air into the lungs, through the nose or mouth by action of the diaphragm.
- To draw air or any form of gas (either in a pure form, or mixed with small particles in form of aerosols/smoke -sometimes stemming from a medicament) into the lungs, through the nose or mouth by action of the diaphragm.
- To eat very quickly.