If you’re like most dog moms, you give heartworm prevention medication because your vet told you to. But do you really know much about heartworm disease? Learn about what causes heartworms, the symptoms, treatment and how you can prevent this life threatening disease.

Causes of Heartwormsblog-heartworm-disease.jpg

There is only one way a dog can get heartworms – by the bite of an infected mosquito. And since there’s no way to tell if a mosquito is infected (not to mention the impossibility of examining these tiny pests), it makes prevention all important.

The bite of just one mosquito infected with the heartworm larvae will give your dog heartworm disease. Veterinarians in the desert states used to say they don’t get heartworm in those areas, but thanks to the boom in building and irrigation, this disease is now reported in all 50 states.

Process and Symptoms

Once bitten by an infected mosquito, it takes about seven months for the larvae to mature into adult heartworms. Then they lodge themselves in the heart, lungs and surrounding blood vessels and begin reproducing. Adult heartworms can grow up to 12 inches long and can live 5-7 years. A dog can have as many as 250 worms in its system. Left untreated, it can lead to a dog’s death.

Initially there are no symptoms. But as more worms invade and crowd the lungs and heart, most dogs will develop a cough. As the disease progresses, they will get more winded with exercise and could even pass out from loss of blood to the brain.


The safest way to treat heartworms includes pre-treatment x-rays and blood work to establish how serious the infection is. Then dogs receive two or three injections of an arsenic-based product to kill the adult heartworms. After treatment, dogs need to be kept quiet for several months. This is because the worms begin to die and break up into pieces, which can block blood vessels and cause death.


Knowing more about this nasty disease, you can see the importance of giving your dog heartworm prevention medication. The American Heartworm Society recommends year-round heartworm prevention for two reasons. First, there is a serious problem with people forgetting to give their dogs the medication. If you give it year-round and forget a month, your dog will probably still be protected. But forgetting two months leaves your dog at risk. The second reason for year-round prevention is that the medication controls intestinal parasites such as roundworms, hookworms, whipworms or tapeworms.

Methods for prevention can be monthly pills, applying a topical to your dog’s skin or getting a 6-month injectable product. The cost of preventative treatment is worth it compared to the damage caused by heartworms and the much higher cost of treatment if infected.

Facts and Myths

  • People cannot get heartworms from their dogs. It can only be passed on by mosquitos. It’s a specific parasite that only affects dogs, cats, ferrets and other mammals.
  • An infected dog cannot infect another dog. Again, it can only be passed on by an infected mosquito.
  • Your dog cannot “outgrow” his heartworms. Left untreated, he stands a good chance of dying.
  • If a dog has heartworms and gets treated, he can get them again. That’s why ongoing prevention is so important.

Learn More – Heartworm Video

If you’d like to learn more, there is a great video provided by Ramona Animal Hospital on You Tube. Go to the Heartworm Video.

This blog is brought to you by Under the Weather™, provider of products for sick pets. Our Chicken & Rice bland diet offers a quick and convenient solution when dogs experience digestive issues such as vomiting or diarrhea. Keep a few bags of this freeze dried formula on hand for peace of mind!

View Our Products

Visit Our Blog Library

Back to blog