What makes chocolate so poisonous to dogs?

I've always heard that chocolate can kill dogs but never knew why. I even seen a show on animal planet where the dog drank some coffee and died of a heart attack while getting surgery at the vet. It was really sad. Can it be the caffine in these products?

not all choclate is poisoness to dogs, I give my mini dachshund organic chocolate and the vet says he is healthy as a horse, its the regular chocolate with all that corn syrup and crap in it that kills dogs, there intestines are not like ours and can't break up certain human foods properly thats why they get sick and die, there intestines get blocked by the food that it couldnt break down.

It's theobromine in chocolate that is poisonous to dogs. Between 250 and 500 mgs/kg, or about 2/3 to 1 1/3 of baking chocolate for every 2.2 pounds of body weight can kill a dog.

Go read this.http://sommerdal.tripod.com/chocolate.htm

Theobromine, a component of chocolate, is the toxic compound in chocolate. (Caffeine is also present in chocolate, but in much smaller amounts than Theobromine.White chocolate: 200 ounces per pound of body weight. It takes 250 pounds of white chocolate to cause signs of poisoning in a 20-pound dog, 125 pounds for a 10-pound dog. Milk chocolate: 1 ounce per pound of body weight. Approximately one pound of milk chocolate is poisonous to a 20-pound dog; one-half pound for a 10-pound dog. The average chocolate bar contains 2 to 3 ounces of milk chocolate. It would take 2-3 candy bars to poison a 10 pound dog. Semi-sweet chocolate has a similar toxic level. Sweet cocoa: 0.3 ounces per pound of body weight. One-third of a pound of sweet cocoa is toxic to a 20-pound dog; 1/6 pound for a 10-pound dog. Baking chocolate: 0.1 ounce per pound body weight. Two one-ounce squares of bakers' chocolate is toxic to a 20-pound dog; one ounce for a 10-pound dog. You can recognize that your dog has eaten a toxic dose of chocolate from the symptoms. Within the first few hours, the evidence includes vomiting, diarrhea or hyperactivity. As time passes and there's increased absorption of the toxic substance, you'll see an increase in the dog's heart rate, which can cause arrhythmia, restlessness, hyperactivity, muscle twitching, increased urination or excessive panting.This can lead to hyperthermia, muscle tremors, seizures, coma and even death.

Caffine is deadly to animals in high doses. It can be coffee, candy or anything else that is with caffine. Small doses usually won't hurt the animal but it is best not to give them any.

http://www.helium.com/tm/93163