Chocolate contains theobromine and a small amount of caffeine, both being stimulants and members of the methylxanthine family. Although it increases alertness, theobromine doesn't have the same jittery effect on the heart like caffeine. However, theobromine can be toxic or even lethal to domestic animals such as dogs, cats, parrots and horses as a result of affecting their kidneys, heart, and central nervous system... Full Text