Heartworm Symptoms In Dogs (And Prevention Tips)

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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 could 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.

Article Overview


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 into 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 but can be done for around $300 in some places. With the right pet insurance plan you can lower that cost even more.


Prevention is so important because 100% of dogs exposed to infective heartworm larvae become infected. Doing your part to prevent heartworms in your dog is the best way to go. You can give your dog monthly pills or apply topicals 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.

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.

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.

Has your dog ever been infected with heartworms?

About The Author:

Kimberly received her Bachelor of Arts in multimedia journalism from Simpson College. She has been writing about dogs since 2014, covering subjects such as dog insurance, training, health, accessories and more. Her natural curiosity helps her research as she seeks the truth when learning about, comparing and personally testing canine products and services. With every piece she writes, her goal is to help our readers find the best fit for their unique needs.

Kimberly grew up in a family that loved Labrador Retrievers and remembers running and playing in the yard with them as a child. In 2017, she and her husband adopted their Coonhound mix, Sally, from a local shelter. Kimberly's research was put to good use since Sally faced some aggression issues with other dogs and needed some training to be an inside dog. She worked daily with Sally and sought help from professionals to help Sally become the happy pup she is today.

One of Kimberly's favorite pastimes is spoiling Sally with new toys, comfy beds and yummy treats (she even makes homemade goodies for her). She tries to purchase the safest products for Sally and knows that each canine has their own specific likes and dislikes. Kimberly is passionate about dogs, and knows the bond between humans and canines is like no other.

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Henry Killingsworth
Thank you for helping me to understand heartworms can make it hard for dogs to exercise. My dog hasn’t wanted to go on a walk with me for at least a week now. It seems like it would be a good idea for me to take him to the veterinarian as soon as possible.
Stephen Bush
The heartworm indisposition is a precarious death-dealing affair that can affect your canine companion frequently. It’s a disease which is transferred from one furry member to other by means of an infected mosquito bite. The inferior part is that after your dog being bitten by an infected mosquito these parasitic worms may migrate to your pooch’s heart and lung, and live there for a longer period of time if not healed timely. Although a dry cough, tiredness after moderate work, the problem in breathing are the common symptoms of heartworm, still there is no such clinical symptom is present. Thus, it is always recommended to take preventive measure by taking an experienced veterinarian consultation to make sure your dog is not going to be infected by the life-threatening heartworm in the first place.
Dee Francis
Thanks for posting these symptoms of heartworm in dogs. I thought that the information in this post for treatments for dogs was really useful. Asking a vet to give my dog injections that can get rid of his heartworm seems really good to know. I found some other useful information in this infographic about the heartworm life cycle,. It has some interesting information that pet owners should know about how female worms release large amounts of microfilariae into the bloodstream, and how they can grow to be twelve inches long. I didn’t know about that before looking at this infographic, so this could also be helpful for other pet owners out there.