My Dog Died After Heartworm Treatment? Possible Causes

Dogs like other pets are susceptible to external and intestinal parasite infestations as they grow. It is a common practice for dogs to wander around. Parasites like ticks, fleas, and even mosquitoes may infest the dogs. One such is the heartworm disease transmitted by mosquitoes.

Heartworm disease is a serious parasitic infection that affects dogs and other animals. It is caused by the parasitic worm Dirofilaria immitis, which is spread through mosquito bites. In this article, you will understand how dogs get heartworm disease, its symptoms, treatment, and more information. Read Up!  

Dog with Heartworm disease

What is Heartworm Disease?

Heartworm disease is caused by parasitic roundworms called Dirofilaria immitis which are transmitted by mosquitos. When an infected mosquito bites a dog, it transfers immature heartworms into the dog’s bloodstream. These worms then migrate to the heart and lungs, where they mature and reproduce.

Inside a new host animal, the larvae migrate through the body over several months, eventually reaching the heart and blood vessels. Here they mature into adult worms, mate, and reproduce, releasing new larvae into the bloodstream.

An infected dog may have dozens of heartworms living in its heart, lungs, and associated blood vessels. The worms cause inflammation, block blood flow, and back up blood trying to get to the lungs. Adult heartworms can reach lengths of up to 12 inches in dogs.

Left untreated, heartworm disease can lead to congestive heart failure, lung disease, organ damage, and even death in dogs. The severity of heartworm disease depends on the number of worms present and how long they have been there. Even just a few worms can impair heart and lung function.

Diagnosing Heartworms in Dogs

Heartworm diagnosis begins with a simple blood test at your veterinarian’s office. This test looks for proteins called antigens that are produced by adult female heartworms. If heartworm antigens are detected in your dog’s blood sample, it indicates an active heartworm infection.

Your veterinarian may also recommend imaging tests like chest X-rays or an ultrasound. These provide a view of the heart and lungs to check for signs of heart and lung disease associated with heartworm infection, such as an enlarged heart or fluid accumulation in the lungs.

X-rays and ultrasounds can also sometimes visualize the heartworms themselves. Some vets recommend running both an antigen test and imaging tests together to confirm diagnosis, as this provides the most accurate results.

Relying on just one or the other can produce false positives or false negatives. Getting the right diagnosis is crucial so your dog can move forward with the appropriate treatment.

Heartworm Treatment Options

The most common treatment for heartworm disease in dogs is called the “slow kill” method. This involves administering a series of arsenic-based injections (typically using Immiticide) over more than 30 days to gradually kill off the adult heartworms.

Veterinarians space out the injections every 2-3 weeks to avoid overwhelming the dog’s system as the worms die off. The dead worms then get absorbed into the dog’s body over time.

Strict cage rest is absolutely critical during the entire treatment period and for some time after. Restricting activity prevents increased blood flow and pressure on the heart and lungs as the worms die, which could dislodge dead worms and cause potentially fatal blood clots or embolisms.

Vets also prescribe anti-inflammatory medications to reduce swelling, inflammation, and side effects as the worms die. Additional medications may be given to protect the dog’s liver and kidneys from the effects of treatment.

Throughout the full treatment, regular blood work, x-rays, and follow-up visits are done to monitor progress and watch for any potential complications.

What Happens if Treatment is Interrupted?

If heartworm treatment is interrupted before completion, the consequences can be serious. The adult heartworms that are still present will continue to cause damage to the heart, lungs, and pulmonary arteries. Larvae will also be able to continue developing into adult heartworms, which can lead to an increased worm burden.

Interrupting treatment essentially allows the disease to progress unchecked. The heart, lungs, and blood vessels will continue to be affected by the damage caused by both adult and immature heartworms. Over time, the disease will worsen if left untreated.

Some of the potential risks of interrupting heartworm treatment include:

  • More extensive lung disease
  • Increased heart enlargement
  • Higher likelihood of pulmonary embolisms
  • Greater risk of congestive heart failure
  • Shorter life expectancy

It is important to follow through with the full treatment protocol. Interrupting treatment places dogs at risk of serious health complications and possible death from heartworm disease. It allows the infestation to proliferate and the effects to compound over time.

Completing the full course of heartworm treatment as prescribed gives dogs the best chance at a full recovery and avoids the impacts of an unchecked infestation. Close adherence to the treatment protocol is key to effectively eliminating heartworms and improving the dog’s health and well-being.

Life Expectancy of Dogs After Treatment

While most dogs have the potential for a full recovery after heartworm treatment, the life expectancy of a dog that has undergone treatment can vary depending on the severity of the disease and how well the dog responds to treatment.

With complete and proper treatment, along with adequate rest and recovery, many dogs go on to live normal and healthy lifespans. Once the heartworms are eliminated, there is usually minimal long-term damage if treatment is started promptly before the disease becomes too advanced.

However, dogs with extremely severe heartworm disease that have been left untreated for an extended period may have a shortened lifespan even after treatment. This can occur when there is substantial heart, lung, and circulatory system damage from the infestation.

These dogs may need more intense treatment protocols and have a tougher road to recovery. Their lifespan may be shortened if the damage cannot be fully resolved. As long as you follow your veterinarian’s recommendations for recovery and provide necessary continuing care, your dog’s prognosis for a normal lifespan is good.

With attentive post-treatment care and prevention, most dogs with even moderate heartworm disease can fully recover and live a normal lifespan.

Related: How to Maximize Your Dog’s Life Expectancy After Heartworm Treatment

Behavior and Activity of Dogs After Treatment

After going through heartworm treatment, dogs require strict rest while recovering. Their activity should be limited to very short leash walks for bathroom breaks. This is to allow the wounds in the lungs and heart to heal without any further damage or stress to the body.

During the recovery period, a dog’s appetite and energy levels may be reduced. They may seem less active, playful, or energetic than normal. However, once the dog has fully recovered, their personality and normal temperament should return. 

As the dog starts to regain strength and healing progresses, exercise can gradually be increased over several weeks. Light walks can be extended and more activity is allowed under supervision. However strenuous exercise should be avoided for at least 4-6 weeks after treatment. Running, jumping, or rough play could reopen wounds or cause further damage.

Eventually, if recovery goes well, the dog should be back to normal activity levels and energy. However, the recovery period requires patience, with activity slowly increasing in a controlled way. Close supervision is needed to ensure the dog does not overexert itself while healing. With proper care after treatment, most dogs make a full recovery.

Risks and Complications

Heartworm treatment carries some risks, especially for dogs with severe infections.

As the worms die, they can block blood flow in the arteries going to the lungs. This is known as pulmonary thromboembolism. If many worms die at once, they can cause life-threatening blockages. Dogs with severe heartworm disease are considered at high risk during treatment for this reason.

There is also a possibility of an allergic reaction to the medication used to kill the heartworms. Reactions may include fever, swollen face, hives, and joint pain. In rare cases, a dog may go into anaphylactic shock. To reduce risks, treatment is broken up into phases and the dead worms are given time to dissolve between each phase.

Other potential complications include inflammation of the lungs, kidneys, or liver. Supportive care helps manage these risks. Your veterinarian will monitor your dog closely during treatment and may hospitalize dogs with advanced infections. With proper care, most dogs recover fully from heartworm treatment.

Prevention of Heartworm Disease in Dogs

Heartworm disease is preventable, so taking measures to protect your dog is the best way to avoid complications from treatment. There are three keys to prevention:

1) Year-Round Monthly Preventatives

– Administering monthly heartworm preventatives year-round is crucial, even in cold winter months when mosquitoes are not as active.

– Heartworm preventatives stop the worms from completing their life cycle. If given consistently, they kill larvae before they develop into adult worms.

– Some options for monthly preventatives include Heartgard, Interceptor Plus, Sentinel Spectrum, or Simparica Trio. Talk to your vet about the best choice for your dog.

2) Mosquito Control and Repellent

– Limit your dog’s exposure to mosquitoes, which transmit heartworms. This might mean avoiding long outdoor activities like hiking or camping during peak mosquito season.

– Use mosquito repellents approved for dogs. Some topical repellents can be applied to your dog’s coat.

– Eliminate standing water in your yard where mosquitoes breed. Make sure water bowls are refreshed frequently.

3) Annual Testing

– Even with preventatives, continue to test your dog for heartworms each year. Catching an infection early makes treatment safer.

– Testing also ensures the preventatives are working properly. It just takes one missed dose for your dog to be vulnerable.

With diligent prevention measures, you can help your dog avoid the risks and complications of heartworm disease and treatment. Protect your pup and give them their best chance at a long and happy life.

Related: My Dog Ate A Burr What Do I Do: Treatment & Prevention Tips


Getting through heartworm treatment can be difficult for dogs and owners alike. This article has covered what heartworm disease is, how it is diagnosed and treated, potential risks and complications, and what to expect in terms of your dog’s life expectancy, behavior, and activity level after treatment.

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