This was taken from YorkieTalk sticky:
"Chocolate/Caffeine:
Chocolate contains theobromine, a compound that is a cardiac stimulant and a diuretic.
After their pet has eaten a large quantity of chocolate, many pet owners assume their pet is unaffected. However, the signs of sickness may not be seen for several hours, with death following within twenty-four hours. Symptoms include Staggering, labored breathing, vomiting, diarrhea, abdominal pain, tremors, fever, heart rate increase, arrhythmia, seizure, coma, death.
Cocoa powder and cooking chocolate are the most toxic forms. A 10-kilogram dog can be seriously affected if it eats a quarter of a 250gm packet of cocoa powder or half of a 250gm block of cooking chocolate. These forms of chocolate contain ten times more theobromine than milk chocolate. Thus, a chocolate mud cake could be a real health risk for a small dog. Even licking a substantial part of the chocolate icing from a cake can make a dog unwell.
Semi-sweet chocolate and dark chocolate are the next most dangerous forms, with milk chocolate being the least dangerous. A dog needs to eat more than a 250gm block of milk chocolate to be affected. Obviously, the smaller the dog, the less it needs to eat."
For More information on toxic foods see
http://www.yorkietalk.com/forums/showthread.php?t=43555
Nancy