Chihuahua Dominance Issues. Spay or neuter your dog to reduce hormonal contributions to aggression. These can include epilepsy, mitral valve disease, and patella luxation.

It is a hereditary disease that usually starts to present about four months after a puppy is born. They will guard their toys, and ignore normal commands. In almost every measure, out of the 35 most common breeds, chihuahuas were reported as the most aggressive, especially toward bigger dogs they have not seen before.