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Heartworm Symptoms In Dogs (And Prevention Tips)


Last Updated: April 21, 2022 | 3 min read | 3 Comments

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Mosquito bites could lead to heartworm symptoms in dogs

Heartworm disease is one of the most dangerous and life-threatening diseases your dog can face. This is why prevention is absolutely key to keeping your pup safe.

Learn about what causes heartworms, the symptoms, treatment and, most importantly, how you can prevent your dog from becoming infected.


Dogs can only get heartworms by being bitten by an infected mosquito. There is no other way. If you’ve heard differently, it’s not true. Not only are mosquitoes tiny but there is also no way to tell if a mosquito is infected with heartworm larvae. This is why preventing heartworms is critical.

After a dog is bitten by an infected mosquito it takes time for heartworm symptoms to appear. After about 7 months, the larvae matures into adult heartworms. The heartworms then lodge in the dog’s heart, lungs and surrounding blood vessels and reproduce. Heartworms can grow up to 12 inches in length and can live 5-7 years. A dog can have up to 250 worms in their body.


  • Coughing
  • Inability to exercise as normal
  • Abnormal lung sounds
  • Passing out from loss of blood to the brain
  • Retaining fluids
  • Death


Before heartworms are treated, a veterinarian will perform an extensive exam including blood work, x-rays and other tests to determine the infection’s seriousness. The dog is then treated with Immiticide, which is an arsenic based product that is injected into the dog. Dogs are given 2 or 3 injections to kill the adult heartworms in the heart’s blood vessels.

All of this work can cost up to $1,000. The cost will depend on the size of your dog, the stage of disease and your location. With the right pet insurance plan, you can lower that cost even more.

Treatment Tips

Here are some additional tips to consider during treatment:

  • Have a detailed discussion with your veterinarian around the time of diagnosis and bring lots of questions.
  • Crate your dog if he/she gets too worked up inside the house.
  • Leash your dog at all times when outside to minimize overexcitement.
  • Keep walks short, especially if it is hot outside.
  • 3-4 month treatment sounds like a long time, but it goes by quickly. Find peace in the knowledge that you are committed to keeping your dog healthy for years after treatment.
  • Several of the heartworm preventative companies offer reimbursement for treatment costs if you can confirm that your dog contracted it while on the medication.


Prevention is so important because most dogs exposed to infectious heartworm larvae become infected. Doing your part to prevent heartworms in your dog is the best way to go. You can give your dog a monthly pill or apply a topical to your dog’s skin to prevent heartworms. You can also give your dog a 6-month injectable. The cost of preventative treatment is worth it compared to the damage that could be caused by heartworms.

The FDA requires a prescription for heartworm medication. And vets usually require a heartworm test to get a prescription, since there is a potential danger for dogs taking the drug if they already have the disease.

Golden being fed drugs by hand with pill box (caption: guide to cheap pet meds)

Once you get a prescription, consider buying ordering medication online to save your next trip to the vet or pet store. Some may even reimburse a portion of the cost of treatment should your pet contract heartworms while on medication purchased from them.

Unfortunately, sometimes a dog can still be infected with heartworms while taking preventative medicine. The main reason this can occur is that the parasite can build up an immunity to the drugs commonly used in their region. It can also happen if you do not administer the preventative appropriately and timely.

Personal Experience

Max and Suzie’s dog, Luna was diagnosed with heartworm at 15 months old, only 3 months after adopting her. She is now 2.5 years old and heartworm negative after completing her full treatment, but it was stressful getting to this day. Here is their experience with diagnosis and treatment.

Luna’s Terrifying Heartworm Diagnosis (Especially While On Preventative!)

Photo of Luna the dog with heartworm

Luna was put on heartworm preventative when she was rescued and tested negative for heartworm at the time of adoption. We continued her heartworm preventative, but there was a window of time for which we couldn’t account. There can be a 6-month gap between an infected mosquito bite and a positive heartworm result (it was probably the 3 months before her rescue).

We heard horror stories about the length of treatment and all the precautions, so we dove in and tried to learn as much as we could about the disease.

Our Treatment Plan

Luna’s treatment involved a series of injections given 1-2 months apart and required her to be monitored by a vet that entire day. It’s crucial to ensure that dogs going through heartworm treatment don’t exercise too much because the lungs start demanding more blood during intense exercise. If a dying worm dislodges during this time, there is a risk that it will migrate to the dog’s lungs and cause a pulmonary embolism, which can be fatal.

During treatment, we took Luna on shorter walks, kept her on a leash when outside and minimized situations where she could get overly excited. One of the difficulties of taking shorter walks was that Luna had much more energy in the house. She was much more active, disruptive and irritable. Eventually, she got used to her new routine, but it took some repetition and consistency.

Getting Luna back to good health was not an easy process, but with a lot of education and patience, we were able to care for her safely and effectively. We are so glad that Luna is back to being her fun-loving, full-of-energy self again.

Heartworm Disease Video

Find out more about heartworm disease in this video:

Heartworms are not the only worms that dogs can get. Learn about roundworms, tapeworms, hookworms and whipworms. Read more about buying inexpensive heartworm preventative medications online and also take action with mosquito repellent for dogs.

The information provided through this website should not be used to diagnose or treat a health problem or disease; it is not intended to offer any legal opinion or advice or a substitute for professional safety advice or professional care. Please consult your health care provider, attorney, or product manual for professional advice. Products and services reviewed are provided by third parties; we are not responsible in any way for them, nor do we guarantee their functionality, utility, safety, or reliability. Our content is for educational purposes only.

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