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Treatment of Heartworms in Dogs

By Jennifer Kvamme, DVM

If your dog is not protected by monthly heartworm preventive medications, he/she is at definite risk of becoming infected with heartworms. This potentially fatal disease could result in your dog having adult heartworms living in his/her lungs and heart, causing many serious problems.

Dogs infected with heartworms will cough, tire easily, and sometimes cough up blood. The symptoms will vary depending on where the worms lodge in the dog’s body and how many of them are present.

Heartworms are transmitted by the bite of an infected mosquito and can only be prevented with heartworm medications that kill off the immature larvae in the dog’s body before they can become adults. Prevention is much easier, safer, and cheaper than treating a case of heartworm disease.

Assessment of Heartworm Disease

heartwormsIf your dog does contract heartworm disease, your veterinarian will determine the stage of the disease (severity) before suggesting a course of treatment for heartworms. There are four stages, or classes of heartworm disease. Class One is less severe and is the easiest stage to treat. Class Four is the stage that is the most difficult to deal with, and these dogs have the worst chance for recovery. Dogs with Class Four heartworm disease need some care before the drugs and treatment can be used to stabilize them. This may involve a surgery where the largest worms are physically removed from the heart and largest blood vessels.

Treatment and After-Care of Heartworm Disease


Before giving any heartworm medication for dogs, your veterinarian will want to look for any underlying conditions in the dog that may cause problems. Chest X-rays will be taken to look for signs of heart disease or lung damage. Blood tests will be run to look for liver or kidney problems that could hamper the dog’s ability to clear the drug from the body. Any problems that are discovered will be dealt with before starting drug therapy.


The most common drug used to treat heartworms in dogs is called melarsomine hydrochloride. The drug is given as a series of injections over a 24-hour period (or separated into two treatments given one month apart). The dog usually needs to be hospitalized for a time during and after the treatment to watch for signs of shock or other adverse reactions that may require further treatment.


After the medication has been given, it will take at least four weeks for the adult heartworms to be eliminated. During this time, the dog will be given monthly heartworm preventive medication to rid the body of the immature worms in the system. Because the worms are dying, they will migrate through the body and be absorbed.


During this time, your dog must be kept from running or playing, as this may cause a rapid movement of a large number of dying or dead worms to the lungs, where they can cause a blockage. For this reason, the dog will need to be watched closely for signs of coughing, vomiting, depression, or diarrhea. Any abnormal signs should be checked by your veterinarian.


Success Rate and the Future after Heartworm Disease


While most dogs (about 98 percent) treated with heartworm disease will clear the infection and not require additional treatment, there is the chance that a second round of medication is needed. It can take many months for the dog to have a negative follow-up heartworm antigen test. If the dog is still positive at six months following treatment, a second dose of medication may be needed.

Treatment for heartworms will not guarantee immunity from ever getting them again in the future. Your dog will need to stay on heartworm preventive medications for life to prevent future re-infection.

Image: AnetaPics / via Shutterstock

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