Chest injuries can be mild, with only a little discomfort on the part of your pet, to life threatening injuries to the lungs and/or heart and lead to collapse of breathing or circulation.
FLAIL CHEST
A flail chest is where several ribs are broken in more than one place. Part of the chest wall is now loose and can more independently to the rest of the chest. When the animal breathes the broken segment will move in the opposite direction to that of the chest wall. This prevents the lungs from expanding and emptying fully, and the animal cannot breath in enough fresh air to obtain oxygen and remove waste carbon dioxide. It is very common in dog bite wounds to the chest.
Use the above techniques to stabilize the chest wall and see your veterinarian immediately.