vet checking for signs of heartworm in a dog
Pet Health Questions and Answers

Signs of Heartworm in Dogs

Of all the infectious diseases that result from parasites attaching themselves to our dogs, heartworm is arguably the most concerning. It must be dealt with as quickly as possible if you suspect that it’s made itself at home within your dog’s internal organs.

Heartworm is a disease that takes its name from parasitic worms that wrap themselves around a dog’s heart. The result of this, as you can imagine, is a painful time for your poor dog.

It’s crucial to note that heartworm is the name of the disease itself, not the parasites that cause it; those go by the moniker of Dirofilaria Immitis. Semantics are not important – the key thing to understand is that heartworm can and should be avoided. Treatment is available, however, if your pet does find themselves struck down by this parasite.

What is Heartworm?

Heartworm is a disease caused by a parasite, not a parasite in itself. It gets confused, much like Frankenstein vs. Frankenstein’s monster!

In this case, the “monster” is a parasite called Dirofilaria Immitis.

Mosquitos carry the parasitic larvae. When an infected mosquito bites your dog, they transfer the larvae. Most times, your dog’s immune system can fight it off—but in larger quantities, these larvae can grow into adult parasites and multiply.

Adult parasites are worms measuring up to twelve inches long! They wrap their way around your dog’s heart and other organs, causing damage and potential organ failure.

Luckily, today’s heartworm treatments are safer and more effective than ever. A relatively new medication called melarsomine cures 95% of dogs treated.

Left untreated, however, heartworm can be deadly.

signs of heartworm

What are the Signs of Heartworm in Dogs?

Speaking of those ill effects, there are seven typical signs and symptoms of heartworm in a dog:

  1. Coughing, especially after physical exercise. This may even expand to fainting.
  2. Weakness, lethargy, and a general disinterest in playing or walking outdoors.
  3. Loss of weight at a rapid and alarming rate.
  4. Panting and difficulty breathing.
  5. Bulges in the ribs and chest.
  6. Sudden allergic reactions to seemingly innocuous items where none have been previously noted.
  7. Collapsing, seemingly out of nowhere.

If you notice any of these symptoms on your dog, get them to a vet ASAP. Time may be of the essence with heartworm – the larvae take a while to mature, but when they do so, they can wreak havoc on a doggy body in record time.

Be aware, however, that heartworm typically unravels in a canine body over four stages, and the very earliest phases of the disease may not come with any visible symptoms. This is why regular testing and preventative measures are hugely important.

These phases typically unfold as follows:

  • Phase I – No physical symptoms.
  • Phase II – Coughing or struggling for breath. Possible lethargy. Heartworm would be diagnosed through a blood test under these circumstances.
  • Phase III – All of the above, but considerably more severe. Your dog will also be less interested in food by this stage and losing weight fast.
  • Phase IV – There is no way of sugarcoating this; a dog with Phase IV Heartworm is dying. Medication will no longer help, and in such a scenario, emergency surgery to physically remove the parasites is the only way to save Fido’s life.

As always, educated is armed in this case – be aware of all of the symptoms of each stage, and seek early intervention if necessary!

vet checking dog for heartworm

What Should I do if my Dog has Heartworm?

If you suspect your dog has heartworm, bring them to the veterinarian right away. Things you can do before and during your appointment include:

  • Limit your dog’s exercise. Rest is key in recovering from heartworm, and unfortunately, your dog will have to get used to a slower lifestyle for a while once they’re diagnosed.
  • Ask for multiple tests. Bloodwork can show false positives, so make sure your dog actually has heartworm before treating them for it.
  • Save as much money as possible. Heartworm treatment is expensive and not always covered by pet insurance.

Once your dog has been diagnosed, follow your veterinarian’s protocol. They can tell you how much exercise your dog should receive and what further treatment is needed.

Depending on your dog’s condition and the severity of the heartworm, this might mean bed rest for up to one month.

How Long Can a Dog Live with Heartworm?

According to Dr. Sarah Wooten, many factors dictate how long a dog can live with heartworm. They include:

  • The size of the dog
  • How healthy the dog is otherwise
  • How their body reacts to the parasite
  • The number of worms in the dog’s system

However, most dogs will die eventually from heartworm if it’s left untreated. Rarely, it might get better on its own—but this will take a toll on your dog’s body, and you should never put off veterinary treatment.

If you’re concerned about the cost, consider asking if your veterinarian offers payment plans. 

For dogs yet to acquire heartworm, look into pet insurance to protect you from the large bills that can wrack up if your dog develops this disease. Of course, also look at prevention!

dog taking heartworm medication

How Can Heartworm be Prevented?

There are several heartworm prevention treatments on the market. They are the best way to keep your dog safe, and your dog should be on them all of the time.

Options for preventing heartworm include:

  • Injections every six months – Your veterinarian can inject a medication called ProHeart 6 or ProHeart 12 into your dog once every six months to one year.
  • Monthly pills – There are various pills on the market to prevent heartworm, including Ivermectin and Heartgard. These are taken once every six months and also protect from various other parasites depending on the medication.
  • Monthly topical treatments – There are also topical solutions available for heartworm, such as Revolution. It works to protect your dog from heartworm, fleas, ear mites, mange, and certain ticks. Topical treatments are applied to the skin on the back of your dog’s neck.
  • Regular testing – Your veterinarian can tell you how often you should test your dog for heartworm based on the medication they’re on and the risk level in your area. Typically, it’s recommended to perform a blood test once every six months.