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A Beginner’s Guide to Dog Heartworm Protection

Petmate Academy

December 9, 2020


As a pet parent, heartworm protection should always be one of your main concerns. But just like any other concern when it comes to your pup's health, knowing the facts is always the best preventative measure.

Let's get right into it.


According to the American Heartworm Society, heartworm disease is a serious and potentially fatal disease in pets in the United States and many other parts of the world. It's known to be caused by foot-long worms (knows as heartworms), which live in the heart, lungs, and associated blood vessels of affected pets. Data from the U.S. Food & Drug Administration also shows that the heartworm disease is most common along the Atlantic and Gulf coasts from the Gulf of Mexico, to New Jerset, and along the Mississippi River and its major tributaries, but it has been reported in dogs in all 50 states.

Heartworms are also quite known to also affect cats and ferrets, but can also live in other mammals, including wolves, coyotes, foxes, sea lions, and on rare occasions, humans.


Heartworms are frequently transmitted from animal to animal by mosquitoes. When a mosquito bites an infected animal, the microscopic larvae of the worm will also be sucked along with the blood of the said animal. The larvae (microfilaria) tend to spend 2 weeks in the mosquito. After 2 weeks, when the mosquito sucks blood again, the larvae will then make its way to the bitten area, and further develop from the inside of its new host.

heartworms transferred from mosquitos



In a span of 2 to 3 months, the worms will then break into a vein, and make its way into the lung artery through the heart. After 6-9 months, the worms will have already mated, releasing eggs through your dog's bloodstream, giving life to even more worms inside your dog's body. Some of the  baby worms die during the disperse, but some survive and continue the cycle.


Your dog will likely appear asymptomatic at first. However, the FDA classified the symptoms into 4 stages.

STAGE ONE: Your dog will exhibit mild symptoms, such as an occasional cough.

STAGE TWO: Mild to moderate symptoms continue, such as lethargy after moderate activity.

STAGE THREE: Your dog will likely begin to exhibit a sick appearance and occasional cough and fatigue after moderate activities. Your dog may experience difficulty in breathing and may begin to develop signs of heart failure. For stage 2 and 3 heartworm disease, these complications can usually be seen on chest x-rays.

STAGE FOUR: This stage is also known as caval syndrome. This is caused by a large mass of worms, which blocks blood flow to the heart. At this stage, quick surgical removal of the heartworms is the only solution.

Other symptoms may include reluctance to exercise, decreased appetite, and weight loss. A swollen belly due to excess fluid in the abdomen may also show in some cases.

It's important to remember that not all dogs with heartworms will end up with caval syndrome. However, if left untreated, mild symptoms can lead to more complicated situations.


dog eating monthly heartworm medication

Just like any other disease, prevention is always better than the cure.

Early diagnostics, whether x-rays or ultrasounds, will do the trick initially. But for a more practical approach, here are some methods you can consider.

A blood sample (on an antigen test) is a viable option, as it detects the agent shed by an adult female worm. A microscopic method of spotting baby heartworms in the blood can also be a way of knowing if your dog has heartworms.

Your vet may recommend monthly chewable pills and an injectable medication that is given every 6 to 12 months.

Outdoor bug control is also a decent option. In general, a clean and organized home is the way to go.

For treatment, the best option is to kill the worms present in your dog. This is not always an easy feat. Veterinarians will always try their best to do what they can while minimizing the side effects of treatment. 

When testing positive for heartworms, you will need to restrict your dog's physical stimulation or exercise, as any intense movement can trigger the heart rate, which could then cause the worms to damage your pet's heart and lungs. Your veterinarian will then provide you with methods you need to follow, and may require placing your dog under a long observation period.


Heartworms are indeed a hassle to both pet parents and pooches. Luckily for all of us, there are solid steps we can rely on in order to prevent heartworms from having their way. As always, regular checkups at the veterinarian are always key to making sure that your dog is in good shape.


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