Mediastinitis in Dogs
 
An inflammation of the mid-chest area is usually caused by a bacterial infection or a fungus. It’s rare in dogs, but in severe cases it may be life-threatening. It is also likely to spread, infecting the bloodstream. Abscesses sometimes develop, and the short vein (called the cranial vena cava in animals) that carries deoxygenated blood from the upper half of the body to the heart's right atrium may become infected. These abscesses can cut off the flow of blood to the heart, resulting in death.
 
Symptoms
 

Gagging
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