According to WebMD, treating a dog that eats chocolate depends on the dog's size and the type of chocolate the animal consumes. Contrary to popular belief, many types of chocolate are relatively harmless to dogs, while others have potentially life-threatening side effects. Because Chihuahuas are very small compared to other dogs, seeking appropriate treatment as soon as possible is paramount.
According to petMD, chocolate is poisonous to dogs due to the presence of a chemical called theobromine. Theobromine is a stimulant similar to caffeine, and it has many of the same effects when consumed. Unlike dogs, humans process theobromine very quickly and efficiently, so they do not experience the negative effects of the substance. However, because a dog's digestive system is poor at processing this chemical, they are at risk of suffering potentially serious side effects. These harmful effects include vomiting, tremors, seizures and even death from cardiovascular disturbances. PetMD does point out that the least processed forms of chocolate, such as cocoa, baking chocolate and dark chocolate, are the most dangerous to pets.
According to WebMD, no amount of chocolate is safe for a dog. Dark and baking chocolates are the most dangerous types because they contain the most theobromine. White and milk chocolates contain less. Citing the Merck Veterinary Manual, WebMD claims that "one ounce of milk chocolate per pound of body weight is potentially lethal" in pets. If the pet consumes dark or baking chocolate, the threshold is much less. Weigh these considerations when deciding whether to seek help. A veterinarian is most likely to pump the dog's stomach and administer sedating drugs to counteract the effects of theobromine, but it is potentially life-saving.