Heartworms and Your Dog

What are Heartworms?

Heartworms are foot-long worms that live in your dog’s heart, lungs, and associated blood vessels. They can cause heart failure, lung disease, and severe damage to other organs in the body.

How are they transmitted?

Heartworms are transmitted through the bite of an infected mosquito. In order to better understand how heartworms are transmitted, let’s take a look into their lifecycle. A heartworm goes through four stages – the first two occur in the mosquito and the last two occur inside the final host.

Mosquitos that bite an infected source suck up baby worms called microfilaria that circulate in the bloodstream of the source. Once inside the mosquito, the baby worms then develop and mature into the “infected stage” larvae over a period of 10-14 days. The mosquito then transfers the infected larvae to a new host, like your dog, when it is bitten.

Once inside the new host, the larvae mature into adult heartworms. This process can take around 6 months and once matured, heartworms can live for 5 to 7 years in dogs.

Signs of heartworms in dogs

-mild persistant cough

-reluctance to exercise

-fatigue after moderate activity

-appetite loss


Dogs with a large number of heartworms may develop a blockage which can lead to cardiovascular collapse called caval syndrome. Caval syndrome is marked as a sudden onset of labored breathing, pale gums, and dark bloody or coffee colored urine. Without emergency surgery to remove the blockage, most dogs do not survive.

Even if your dog isn’t showing any of these signs, it doesn’t necessarily mean your dog does not have heartworms. Most dogs don’t show any symptoms in the early stages of the disease, however, the longer the infection persists, the more likely symptoms will appear.

Testing and prevention

All dogs should be tested annually for heartworms and should be on heartworm medication as soon as possible.¬†Because heartworms can live up to 7 years, each mosquito season can lead to an increasing number of worms in an infected pet, so it’s important that your dog be on heartworm prevention.Talk to your veterinarian if you have future questions prevention.


If your dog tests positive for heartworms it can be treated. Your veterinarian will first want to stabilize your dog if he is showing signs of disease. They may also recommend that your dog be on antibiotics before treating the heartworms. Once your dog is stable, your vet will follow the guidelines set by the American Heartworm Society to attack the heartworms. Around 6 months after treatment is completed, your dog should be tested again to confirm that all heartworms have been eliminated.


Recovery can take months and it is very important that your dog take it easy until completely healed. Your dog may be lethargic from the treatment but if he is not, that doesn’t mean its okay to resume normal activities. Restrict their exercise, physical exertion increases the rate at which the heartworms cause damage in the heart and lungs. If your dog doesn’t want to eat his kibbles, try making a dog-friendly soup for them, if they still won’t eat contact your veterinarian.