Cats and Chocolate
Theobromine, a substance present in chocolate and cocoa, is poisonous to animals. It diminishes the blood flow to the brain and can cause heart attacks and a variety of other life-threatening problems. An important rule to remember is that the darker the chocolate, the more theobromine it contains. If you know your cat has eaten chocolate, contact your veterinarian immediately.
Fortunately, most cats are not so attached to chocolate that they will eat it in large quantities. Many cats, however, will eat enough if curious, bored, or encouraged to do so because their well-meaning owners, especially the younger members of the family, believe that they are giving their pet a treat. It is best to keep chocolate out of the reach of children and their pets