Yes, chocolate is poisonous to dogs. Symptoms are vomiting, diarrea, high body temperature, seizures, low blood pressure and rapid breathing. For milk chocolate on average it will take about 0.7 oz per pound of dog's weight of chocolate for dogs to experience toxicity. For semi-sweet chocolate it only takes 0.3 oz. For baking chocolate it takes 0.3 oz, too.-John Baskin
Information from: http://www.petmd.com/dog/conditions/digestive/c_multi_chocolate_toxicity#.T0lv43JSS7Y
