chocolate is bad for dogs because it contains the alkaloid ,theobromine that stimulates the central nervous system, cardiovascular system and causes increased blood pressure. Dogs and other animals, such as horses and cats, can't digest theobromine as quickly as humans can and too much of this alkaloid in an animal's system can lead to diarrhea, vomit, increased urination, muscle twitching, excessive panting, hyperactive behavior, dehydration, digestive problems, seizures and rapid heart heart rate. Now do you see why it's not a good idea to give your pet chocolate?