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Today is: Wednesday January 17, 2018

Heartworm and Your Dog

Photo from www.placervillevet.com

Heartworm disease is a common problem throughout the world. Heartworms are parasites that inhabit the heart and lungs of dogs, and cats. Dogs can be infected as young as four to six months old. Heartworms can cause very serious problems and if not promptly and properly treated it may lead to heart failure and/or death. Treatment of heartworms is risky and expensive, prevention is easy. Heartworms are only transmitted through infected mosquitoes. And, it only takes just one bite from an infected mosquito to transmit this disease. All dogs living in an area where heartworm exists are at risk, even if the live entirely indoors.

There are various preventative treatments available. Heartgard is a common choice. This is a once a month oral treatment that you give to your dog. Revolution is also a monthly treatment, this is a topical product that is given in the shoulder area. There is also a six month shot that is available, Proheart 6.


Transmission occurs when a mosquito bites an infected dog and ingests heartworm larvae, which live in the bloodstream. When the infected mosquito then bites an uninfected dog, some of the heartworm larvae are injected under the skin. The larvae then grow for three to four months, eventually making their way into the heart, where they develop into adults. Once in the dog's heart, the worms can grow to seven to 11 inches in length and cause significant damage to the heart and lungs.


Symptoms don't usually occur until damage has already occurred in the heart, namely heart failure. Dogs can have a wide range of symptoms, to no symptoms at all. Symptoms include:

  • Decreased appetite

  • Weight loss

  • Listlessness

  • Coughing

  • Coughing up blood

  • Heavy breathing

  • Unwillingness or intolerance to exercise

  • Fluid distention of the belly

  • Pulsation of the jugular vein in the neck when the dog is sitting or standing


Blood tests are used to confirm heartworm disease. Once diagnosed, your vet will determine what stage your dog is in. A complete physical exam will be given. A complete blood panel is usually drawn. Chest x-rays will be done to determine how severe the disease is. An evaluation of the heart will be done. This could include an ultrasound of the heart and an electrocardiogram (ECG).


Treatment will involve killing both the adult and baby (larvae) heartworms. There are two main drugs administered by vets for heartworm treatment. They are:

  • Melarsomine (ImmiticideŽ) - This drug is given by injection deep into the muscles of the back. This drug is less likely to cause side effects than the other drug. This treatment is the most common type of treatment. Treatment protocol depends on the severity of infection. Dogs with mild cases are treated once daily for two days. For more severe cases, the dog is given one injection, then 30 days later is treated once daily for two days. Four months after treatment the dog should have a blood test done to check for antigens. Some dogs may need a second treatment.

  • Thiacetarsamide Sodium (CaparsolateŽ) - This drug is given in the vein through a catheter. Some dogs get very ill with this drug. Therefore, sometimes treatment needs to be stopped. Usually hospitalization is necessary during this treatment.

  • Surgery - Occasionally surgery is performed to remove the worms from the heart.

Both drugs contain arsenic. Regardless of which drug is used, when the adult heartworm dies it may obstruct the blood vessels in the lungs, this is called a pulmonary embolism.

After treatment care

Because of the risk of a pulmonary embolism, it is very important to restrict the activity and exercise of the dog. These restrictions must be closely followed for four weeks after treatment. If at all possible, cage rest would be the ideal resting place. Keeping the dog quiet allows time for the body to slowly break down and absorb the dying worms.

Sometimes aspirin is prescribed as an anti-inflammatory to help minimize the reaction in the lungs to the death of the worms.

Prednisone can be given pre-treatment for extreme lung inflammation and severe coughing. It can be administered post-treatment for treatment of complications, listed below.

After treatment complications

The most common and most dangerous complication is pulmonary embolism. Signs associated with pulmonary embolism are:

  • Fever

  • Heavy or fast breathing

  • Coughing

An occasional complication with the injection treatment is back pain.

If any of the signs are observed it is important to get your dog to the vet immediately to be evaluated.

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 --not a substitute for-- 
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