Chocolate contains methylxanthines, stimulants that stop a dog’s metabolic process. Even just a little bit of chocolate, sometimes just the smell of rich dark cocoa, can cause diarrhea and vomiting. A significant amount can cause seizures, irregular heart function, and even death.
If you so much as suspect that your dog may have had access to a single chocolate chip, contact a veterinarian or Pet Poison Helpline immediately.