It can, depending on their weight and how much they eat, so be vigilant this Valentine’s Day. Stimulants in chocolate can lead to vomiting, diarrhea, agitation and life-threatening elevated heart rates or seizures.

“Dogs have no off button,” said Dr. Tina Wismer, the medical director of the ASPCA Animal Poison Control Center. “If you or I ate 10 percent of our body weight in chocolate, we’d have the same problems. A 10-pound dog can easily eat a pound of chocolate.”

The darker the chocolate, the more toxic it is. For a 20-pound dog, 9 ounces of milk chocolate can cause seizures, but it takes only 1.5 ounces of baker’s chocolate, she said.

Signs of chocolate poisoning usually appear six to 12 hours after ingestion, according to The Merck Veterinary Manual.

“Seizures due to toxicity don’t stop unless you treat them,” Dr. Wismer said. So head to the emergency clinic or veterinarian if you come home to find your dog vomiting repeatedly and extremely agitated, and certainly if the pet is unconscious and its limbs are shaking. By contrast, dogs who vomit once and fall sleep can be watched at home, she said.

Unlike cats, dogs like sweets. So it’s best to keep chocolate stored away and off countertops, which are no match for a motivated climber.

Carob treats are a safe alternative for dogs who love the flavor of chocolate. Other common foods that pose hazards to dogs are raisins and grapes. Xylitol, used to sweeten sugarless gum, is also “a big problem” for a pet, Dr. Wismer said, “It actually drops his blood sugar, and he can have seizures.” Catherine Saint Louis.

Different types of chocolate contain different amounts of theobromine: It would take 20 ounces of milk chocolate to kill a 20-pound dog, but only 2 ounces of baker's chocolate or 6 ounces of semisweet chocolate. It is not that hard for a dog to get into something like an Easter basket full of chocolate eggs and bunnies and gobble up a pound or two of chocolate. If the dog is small, that could be deadly.