How do deer breathe?

Deer breathe with their lungs, just like humans and other mammals. They have a diaphragm that separates the thoracic cavity from the abdominal cavity, and when the diaphragm contracts, it pulls air into the lungs. The lungs are filled with tiny air sacs called alveoli, where oxygen is exchanged for carbon dioxide. The oxygen-rich blood is then pumped throughout the body by the heart.