arteries in the lobes of the lung. Inflammation of the lung tissue is also often observed. Treatment in dogs If an animal is diagnosed with heartworms, treatment may be indicated. Before the worms can be treated, however, the dog's heart, liver, and kidney function must be evaluated to determine the risks of treatment. Usually, the adult worms are killed with an arsenic-based compound. The currently approved drug in the US, melarsomine, is marketed under the brand name Immiticide. It has a greater efficacy and fewer side effects than the previously used drug thiacetarsamide, sold as Caparsolate, which makes it a safer alternative for dogs with late-stage infections. After treatment, the dog must rest, and exercise is to be heavily reduced for several weeks so as to give its body sufficient time to absorb the dead worms without ill effect. Otherwise, if the dog is under exertion, dead worms may break loose and travel to the lungs, potentially causing respiratory failure and sudden death. According to the American Heartworm Society, the administering of aspirin to dogs infected with heartworms is no longer recommended due to a lack of evidence of clinical benefit, and aspirin may be contraindicated in several cases. Aspirin had previously been recommended for its effects on platelet adhesion and the reduction of vascular damage caused by the heartworms. The course of treatment is not completed until several weeks later, when the microfilariae are dealt with in a separate course of treatment. Once heartworm tests are negative and no surviving worm is detected, the treatment is considered a success, and the patient is effectively cured. Surgical removal of the adult heartworms as a form of treatment may also be indicated, especially in advanced cases with substantial heart involvement and damage. Prevention of infection in dogs Prevention of heartworm infection can be obtained through a number of veterinary drugs. The drugs approved for use in the US are ivermectin (sold under the brand names Heartgard, Iverhart, and several other generic versions), milbemycin (Interceptor Flavor Tabs and Sentinel Flavor Tabs) and moxidectin (Simparica Trio) administered as chewable tablets. Moxidectin is also available in both a six-month and 12-month sustained-release injection, ProHeart 6 and ProHeart 12, respectively, administered by veterinarians. This injectable form of moxidectin was taken off the market in the United States due to safety concerns in 2004, but the FDA returned a newly formulated ProHeart 6 to the market