Dog owners in Derby are being urged not to feed their pets chocolate meant for humans over the festive period.
Many owners do not realise that this kind of chocolate is highly toxic to dogs, Derby City Council said.
It contains a stimulant, Theobromine, which can affect the central nervous system and the heart muscle.
In 2007, 1,166 emergency calls were made by vets to dogs suffering from chocolate poisoning. In 2006, 790 such calls were made.
Symptoms include hyperactivity, agitation, excessive thirst, breathlessness, diarrhoea and vomiting.
The Christmas holiday period can be particularly bad since dogs can steal chocolate ornaments from the tree, eat edible presents or are fed by well-meaning owners and visitors, Derby City Council said.
Cabinet Member for Housing and Public Protection, Councillor Robert Troup, said: ''Our advice to owners is to keep chocolates out of reach and buy special chocolate dog treats from pet stores.
"If you know your dog has eaten a large amount of chocolate don't wait for the symptoms to appear. Take them to the vet straight away.''