Why is chocolate bad for dogs?

Chocolate can contain high amounts of fat and caffeine-like stimulants known as methylxanthines. If ingested in significant amounts, chocolate can potentially produce clinical effects in dogs ranging from vomiting and diarrhea to panting, excessive thirst and urination, hyperactivity, abnormal heart rhythm, tremors, seizures and even death in severe cases.

Typically, the darker the chocolate, the higher the potential for clinical problems from methylxanthine poisoning. White chocolate has the lowest methylxanthine content, while baking chocolate contains the highest. As little as 20 ounces of milk chocolate—or only two ounces of baking chocolate—can cause serious problems in a 10-pound dog. While white chocolate may not have the same potential as darker forms to cause a methylxanthine poisoning, the high fat content of lighter chocolates could still lead to vomiting and diarrhea, as well as the possible development of life-threatening pancreatitis, an inflammatory condition of the pancreas.

Source: ASPCA

Has your dog ever gotten into chocolate? What symptoms did your dog have?