Signs and Symptoms of Heartworm in Dogs

Ah, the weather is finally warm and sunny - perfect for long nature walks with your dog. However, with warm weather come nasty mosquitoes that can completely ruin your relaxing outing. Yes, they are annoying, but they also might carry a bigger problem that can affect your dog - heartworm!

So, if you live in a mosquito-filled area, make sure to learn about these nasty parasites and know the signs and symptoms of heartworm in dogs.

Get to Know the Enemy

All pet owners know about heartworm, but what is it exactly? Well, Dirofilaria immitis or heartworm is a type of roundworm that lives in an infected dog’s heart, lungs and surrounding veins.

If an infected mosquito bites your pup, it can inject the young heartworm into the dog’s body and cause heartworm infestation. These worms can stay alive inside these organs for many years and reach the size of almost 12 inches! 

Needless to say, heartworm causes many health issues in pets and can even cause death if untreated. And even though it’s mostly present in dogs, cats and other pets can also be transmitted this nasty parasite!

Pup with heart disease

Recognize the Symptoms

Some dogs show bigger symptoms while some dogs show them only when it’s too late, so make sure to know exactly what to keep your eye on.

Most symptoms don’t even appear until the worm reaches maturity which is usually after six months from the mosquito bite.

Unfortunately, symptoms listed below can also signify other health issues, which makes it even more difficult to recognize heartworm!

Lung Issues

One of the most obvious symptoms of heartworm is coughing that occurs as parasites enter the lungs and surrounding blood vessels.

Coughing fits are especially strong during and after exercise and can even cause fainting! There are other breathing problems that occur as the worms enter the lungs.

Difficulty breathing is also present!

Fatigue and Weight Loss

Heartworm causes weakness and fatigue, so if you suddenly notice your active pup doesn’t want to go for a walk or play with you, make sure to see the vet.

Even small tasks like eating or drinking water can become too difficult to perform which leads to drastic weight loss.

Unusual Rib-cage Shape

Heartworm causes fluid buildup which can create the appearance of a bulging rib cage in your dog. Additionally, your pup might lose a lot of weight which can also contribute to this anorexic look.

So, make sure to pay attention to any changes in your pet’s appearance.


Once heartworm gets into the heart and blood, it will block blood flow which causes collapsing. But, if you notice any seizures, wobbly walk, lameness or blindness, this might mean the parasites have reached the brain.

This is the most dangerous stage of the infection that usually ends fatally if you don’t start treatment.

Dog getting checked at the vet for heartworm

Test in Time

If you suspect your dog might be infected, don’t do anything yourself, but visit your vet. They will take your pet’s blood sample and check it for heartworm antigens.

Your pet might also need to have its x-ray taken, so the vet can check of any heart, artery and lung swelling.

In case the worms have entered the heart, an ultrasound can help determine the damage and tell the doctor if your pooch is ready for treatment.

Prevention is Key

You can’t really protect your pooch from ever getting bitten by a mosquito, but what you can do is protect it from heartworm!

Luckily, there are many different pills you can find in stores or online shops that sell various dog supplies and medication. These pills have to be taken monthly or every three to six months and are super easy to administer - some come in the shape of chewables that dogs just love! 

Most importantly, though, they are very successful in preventing heartworm and keeping your pup healthy and strong!

There are also spot-on treatments, but pills are much easier to give to your dog and have a better effect.

The Course of Treatment

In case your vet diagnoses heartworm in your pup, don’t despair as nothing is lost yet. Depending on how serious the infection is, your dog can be cured of these parasites.

Usually, the aim is to kill all adult worms and prevent offspring from maturing. Sometimes, vets even have to take a surgical route to remove heartworm from the organs!

The whole treatment is long, exhausting, painful and expensive, so prevention is always the way to go!

Final Thoughts

Now that you know the signs and symptoms of heartworm in dogs, you'll be ready to act fast and give your pup appropriate prevention or a quick recovery.

It’s important to stay alert, administer prevention regularly and act as soon as you see anything suspicious in your four-legged friend and your pet will be healthy, happy and strong for many years to come!

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