Because treatment for worms can be both dangerous for the pet and expensive for the owner, preventing worms is the best way to deal with the problem. Cats and dogs are susceptible to at least two kinds of worms: intestinal and heart worms. Your veterinarian can give blood tests for these worms, which should be done at least yearly so that prompt treatment can begin if they are found. Worm larvae (lar-vee) can be ingested by your pet in infected feces (fee-sees) and through some mosquito and flea bites. Intestinal worms are usually seen on a pet's feces, but heart worms can only be detected through blood tests or severe symptoms such as weakness and weight loss. While intestinal worms are easily treated, heart worms are more serious and can be fatal. Protect your pet against worms with medication and information from your veterinarian.