Chocolate contains a derivative of caffeine called theobromine. Dogs are unable to digest theobromine and ingestion can lead to hyperactivity, tremors, panting, racing heartbeat, vomiting, diarrhoea and seizures. Unfortunately, it can be fatal for some dogs.
As a general rule, the darker the chocolate, the more toxic it is.
If your dog has ingested ANY chocolate, big or small, you need to seek veterinary attention immediately. This way if we are able to make your dog vomit we can prevent any nasty side effects.
Not sure how much is too much when it comes to chocolate? Here’s a tool you can use kindly provided by Petcare which easily shows how much chocolate is too much for a dog.