If your dog begs for chocolate, don't give in! Chocolate contains theobromine, a naturally occurring stimulant found in cocoa beans that can cause vomiting, heart problems, seizures, and even death for dogs. How much chocolate is too much? It depends on the type of chocolate and the weight of the dog. Find out how much of each kind of chocolate can harm your pet by consulting the National Geographic Magazine Chocolate Chart. Scroll on the page to change the weight of the dog and the type of chocolate.