Chocolate contains theobromine, a compound that is a cardiac stimulant and a diuretic. When affected by an overdose of chocolate, a pet can become excited and hyperactive. Theobromine will either increase the dog’s heart rate or may cause the heart to beat irregularly. Death is quite possible, especially with exercise.
After a pet has eaten a large quantity of chocolate, many owners assume their pet is unaffected. However, the signs of sickness may not be seen for several hours, with death following within 24 hours.
Cocoa Powder & cooking chocolate are the most toxic forms. A 10-kilogram dog can be seriously affected if it eats a half of a 250gm block of cooking chocolate. Even licking a substantial part of the chocolate icing from a cake can make a pet unwell.
This includes cakes with the above ingredients especially mud cakes. Read more about chocolate toxicity here