Heartworm in dogs – how to keep your dog safe

Heartworm in dogs is a disease caused by an internal blood parasite called Dirofilaria immiti. It’s widely spread and in my opinion underestimated. It requires long treatment, is potentially fatal, and is preventable.

Somehow, a lot of people know that dogs can get infected with heartworm.

However, from my experience, it’s more of an “I’ve heard that something like that exists” than an “ok, how do I protect my dog” kind of thing. This is not a good way of thinking when we’re talking about a preventable life-threatening disease that is endemic in many places 😟

I also firmly believe that it’s up to every veterinarian to educate his clients and talk about the risks. Especially during the summer travel season.

But since you landed on my blog, here’s a complete guide for you 🤗

While I am a veterinarian, this article is not intended to replace professional veterinary advice. If you have any medical concerns about your pet, consult your vet immediately. Always seek professional assistance if you are unsure of your pet’s health.

This post may contain affiliate links, which means I may receive a commission, at no extra cost to you, if you make a purchase through a link. Please see my full disclosure for further information.

Blog post pictures 4

How do dogs get heartworm

In my previous posts, I talked about diseases transmitted by ticks. Some people think ticks are also carriers of dirofilariasis. This is not the case. 

Heartworm is transmitted by mosquitos, which carry the heartworm larvae from one host (a dog, cat, ferret…) to another.

A mosquito bites an infected host and ingests the first stadiums of heartworm – microfilariae.

These transform into infectious larvae inside the mosquito and when he bites your pet they get injected into his bloodstream.

The larvae then continue to develop in your dog’s tissue. This process takes around 2 months.

Once the larvae are mature enough, they leave the tissue as developing adults and travel in your dog’s bloodstream, into the blood vessels that serve the heart and lungs, and in advanced infections also directly into the heart.

Larvae need another 5-7 months to turn into mature adults capable of producing microfilariae.

These adults stay permanently lodged in blood vessels that serve the heart and lungs and in the heart itself. These adult parasites can live up to 7 years.

When your dog gets now bitten by another mosquito, it ingests the microfilariae from your pet’s blood and the whole cycle begins again.

So essentially, mosquitos are vectors – they carry the larvae from one animal host to another. But without them, the whole cycle would not be possible. 

One infected animal cannot directly infect another animal or a human. So the spreading of heartworm is directly correlated with mosquito incidence.

Several studies have shown that the incidence of heartworm in dogs is rising (for more information see references at the bottom 🙂). The main factors that have influenced the spreading of heartworm infections are climate changes and new invasive mosquito species. 

Nowadays, heartworm in dogs is endemic in many places, including Canada, many USA states, Europe, and southeastern regions of Asia.

Heartworm is a parasite disease that needs a mosquito to be able to spread. You cannot catch heartworms from your dog. However, there are a few other diseases you can get from a dog.

Symptoms of heartworm in dogs

Heartworms that are lodged in blood vessels and the heart cause irritation and inflammation. Your dog’s immune system may cause further damage, especially in response to dead worms. The constant irritation can lead to scarring and reduced flexibility of blood vessels.

Many dogs show no or just a few mild symptoms in the early stages of the disease. However, the longer the infection persists, the more severe the signs will get.

Symptoms of heartworm in dogs may include:

  • coughing (mild or persistent)
  • reluctance to exercise
  • decreased appetite
  • fatigue
  • fainting
  • labored breathing
  • blue discoloration of the gums
  • accumulation of fluid in the abdominal cavity

Additionally, blood clots, dead worms, or a large number of worms can block blood vessels and/or the heart, which can lead to a cardiovascular collapse. This condition is called caval syndrome.

Caval syndrome is a medical emergency. At this stage, the dog needs immediate surgical intervention, or he will most likely die.

Diagnosis of heartworm in dogs

Heartworm is a progressive disease. This means that the sooner we know about it, the better the prognosis.

There are a few options for diagnosing heartworm in dogs. The most specific and largely used is an antigen detection test. It’s easy to perform and reliable.


However, it cannot detect the very early stages of the infection. That’s why your vet may recommend regular yearly testing.


In any case, once a dog has a positive test, further diagnostic tests are needed to confirm the diagnosis.

heratworm in dogs - vetcarenews

Treatment of heartworm in dogs

The treatment depends on multiple factors, such as your pet’s prior medical history, concurrent health conditions, the severity of the infection, and the extent of the heart and blood vessel damage.

The goal is to stabilize your pet and kill the adult and immature parasites. Before the actual heartworm treatment, your vet may prescribe medications to stabilize the heart and lungs.

There are specific approved protocols and guidelines for treating heartworm in dogs.

Dead worms pose a high risk of severe respiratory problems.

The signs include coughing, spitting up blood, labored or rapid breathing, lethargy, lack of appetite, and fever.

Such patients need cage confinement, with several days of oxygen treatment and drugs to control inflammation and reduce blood clotting.

The risk of post-treatment complications can be reduced by confining the animal or/and restricting his activity throughout the treatment and 4-6 weeks after. I know it’s hard, but it can’t be helped  😔

Sometimes there are so many heartworms in a dog’s heart they need to be removed surgically.

To summarize, the treatment of heartworm in dogs consists of:

  • stabilizing the patient
  • actual heartworm treatment with an approved protocol
  • activity restriction or confinement
  • surgery (in extreme cases)

Your dog needs to be tested again 9 months after the treatment to confirm that all parasites have been killed and eliminated. I would recommend testing your dog every year.

Heartworm prevention for dogs

As I said before, heartworm disease is preventable. There are several approved drugs that can be used safely.

Most of the preventive products need to be given monthly, so please set a reminder in your calendar. The most common mistake pet owners do is that they forget to administer the medication or use expired products.

I would recommend starting with preventive care as early as the product label allows, especially if you live in an area where heartworm is endemic. Furry babies are not immune, and the risk of contracting the disease is the same as in adult pets.

The products are usually dosed according to body weight, so there is no need to be afraid of overdosing your new family member. Talk to your vet about preventive care for your puppy.

Products you can use to protect your dog:

As you know, it’s important to regularly deworm your dog. Not just for his but also for your own protection.

And because we live in such an awesome age, you can now buy products that will kill the most common intestinal parasites, and protect your pup against fleas, ticks, and heartworm 😎


There are several products on the market you can choose from, for example, Revolution For Dogs (spot-on), Advantage Multi (Advocate) for Dogs (spot-on), or Heartgard Plus for dogs(chewable).


They need to be given monthly to be effective against heartworm. 

I’m one of those people who forget everything, so I’ve set multiple reminders on my phone ☺️


Just be aware that while they are effective against roundworms, whipworms, and hookworms, they don’t treat tapeworm infections!

Heartworm in dogs is a progressive disease caused by an internal blood parasite. It’s potentially fatal with symptoms similar to heart disease.

The longer the infection persists, the more serious the symptoms are.

The treatment needs to be administered accordingly to approved protocols and guidelines.

As I said before, it’s a potentially fatal disease that is actually preventable. So please, please, please, use approved preventive products and let your dog get tested once a year.

Especially if love traveling with your furry friend. This way you can enjoy those trips without unnecessary risks 😎

Stay safe! 🥰

PS: Are you as crazy about animals as I am? Do you want to get regular pet health tips in your inbox? Subscribe to my newsletter and get a free pet care planner as a bonus 🤗


– Genchi C, Kramer LH. The prevalence of Dirofilaria immitis and D. repens in the Old World. Vet Parasitol. 2020 Apr;280:108995. doi: 10.1016/j.vetpar.2019.108995. Epub 2019 Nov 21. PMID: 32155518.
– Drake J, Wiseman S. Increasing incidence of Dirofilaria immitis in dogs in USA with focus on the southeast region 2013-2016. Parasit Vectors. 2018 Jan 17;11(1):39. doi: 10.1186/s13071-018-2631-0. PMID: 29343304; PMCID: PMC5773159.

Leave a Reply

Your email address will not be published. Required fields are marked *