Most likely a respiratory infection IE: a cold
Try adding a few drops of cider vinegar to his water supply. About 1 tablespoon per gallon should be enough. This will help him clear mucus from his system. You can also buy water soluble tonic specifically for easing cold symptoms in chickens from the same source you obtain your chicken feed/supplies.
These are diaphragm and externa intercostal muscles in quiet breathing and sternocliedomastoid ,sclene muscles,anterior serrati in heavy breathing
heavy breathing occurs to breathe out the acid (CO2) in an attempt to correct the acidosis.
heavy breathing as you call it , in an engine would mostly be caused by a filthy air cleaner or a blocked air intake
Heavy breathing in a Shar Pei can be caused by various factors, including heat, anxiety, or exercise. Due to their unique facial structure, they are also prone to respiratory issues, which can exacerbate heavy breathing. If the heavy breathing persists or is accompanied by other symptoms, it’s essential to consult a veterinarian to rule out any underlying health concerns. Always ensure your Shar Pei stays cool and calm, especially in warm weather.
dying
aches in the muscles and heavy breathing
Heavy breathing can be a sign of many things, including that she may be in labor and ready to have her foal. Heavy breathing most commonly means the horse is uncomfortable or has exercised heavily. Mares who are in labor will breathe heavily. Mares who have a foal inside them that is in an awkward position will also be uncomfortable and sometimes breathe heavily.
The doldrums have heavy precipitation,little wind
If you have a heavy chest feeling that is not tight and you are having no breathing issues, it should still be checked out. It could be something as simple as acid reflux but it could be more severe.
See a vet, immediately!
Melanie Comber has written: 'Heavy breathing'
pore kitty take it to the vet