Chocolate contains Theobromine, which dogs are not well able to break down. Please keep chocolate away from your best friend.
Theobromine stimulates the cardiovascular and central nervous systems. Signs usually occur within twelve hours of ingesting the chocolate and can include: vomiting and diarrhoea, trembling and muscle spasms, increased excitement, irritability or nervousness, elevated heart rate, excessive thirst and urination, seizures, coma and possibly death due to cardiac disturbances.
Different types of chocolate contain different amounts of Theobromine. Symptoms are usually seen after ingesting: 60 grams per kg of milk chocolate and 7 grams per kg of unsweetened dark chocolate. White chocolate contains negligible amounts of Theobromine, making toxicity unlikely.
There is no antidote for chocolate toxicity, so only supportive treatment can be given. If you suspect chocolate has been consumed, call your vet to arrange for vomiting to be induced.