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How to Check If Your Dog Has Heartworms: An Expert Guide

heartworms in dogs

Knowing how to check if your dog has heartworms could potentially save a life. Heartworm disease is a potentially fatal condition affecting dogs of all ages. These nasty spaghetti-like parasites can cause damage to the heart, lungs, and other vital organs, and if left untreated, can lead to death.

Fortunately, heartworm disease is treatable if caught early. The first step in protecting your dog is knowing all the signs. Additionally, since heartworms spread through mosquitoes, be sure to keep your pup’s bed in a mosquito-free space in the house if your area has these pesky insects.

This article will discuss how to check if your dog has heartworms, including the types of tests available and what to do if your dog tests positive. We have the help of expert sources like Joseph Bottone’s Heartworm Survival Guide for an extensive dog heartworm guide.

Multiple insects can ravage dogs and spread disease. So owners are constantly checking if their dog has fleas and questioning if bugs like spiders and bed bugs. Of all these bugs, you could say heartworms are the most severe insect-transmitted disease.

The heart disease results from a parasitic worm called Dirofilaria immitis, transmitted through an infected mosquito’s bite. Studies show it’s common along the Atlantic and Gulf coasts from the Gulf of Mexico to New Jersey and along the Mississippi River, but it can occur in all states.

Step-by-step Guide To Checking A Dog For Heartworms

dog heartworms

Here’s a quick run through how to check if a dog has heartworms:

  1.  Look for Signs 

    Dogs with heartworms always display a dry, persistent cough, like something is stuck in the throat. Other signs include weakness, weight loss, breathing difficulties, and fatigue after mild activity. We delve deeper into heartworm signs in dogs in the following section.

  2. Physical Examination

    The second step in diagnosing heartworm disease is a physical examination by a veterinarian. During the examination, the vet will look for signs of heartworm infection, such as a persistent cough, difficulty breathing, and abnormal lung sounds. They will also check for other symptoms like lethargy, weight loss, and decreased appetite.

  3. Blood Test

    If the veterinarian suspects heartworm disease, they will perform a blood test to confirm the diagnosis. The test detects the presence of heartworm proteins in the dog’s blood. If the test is positive, the vet will perform additional tests to determine the severity of the infection and the best course of treatment.

  4. Imaging Tests

    Imaging tests like X-rays and ultrasounds may also be used to diagnose heartworm disease. These tests can help the vet see the extent of the damage to the dog’s heart and lungs. They can also help determine if there are any complications, such as fluid buildup in the lungs.

  5. Preventive Measures

    Preventive measures, such as monthly heartworm medication, are the best way to prevent heartworm disease. These medications are available in different forms, including chewable tablets, topical treatments, and injections. It’s important to follow the vet’s recommendations and administer the medication as directed.

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Understanding Heartworms

What Are Heartworms?

Heartworms are parasitic worms that live in the heart, pulmonary artery, and adjacent large blood vessels of infected dogs. They spread through the bite of an infected mosquito and can cause serious health problems in dogs. 

Heartworms can grow up to a foot long and can cause blockages in the heart and lungs, leading to difficulty breathing, coughing, and even death if left untreated. Female heartworms grow up to 10 to 16 inches long (25 to 39 cm), and males to 4 to 6 inches (10 to 15 cm).

How Dogs Get Heartworms?

Dogs can get heartworms when an infected mosquito bites them. The mosquito picks up the larvae of the heartworm from an infected animal and then transmits the larvae to the dog when it bites. Infected dogs cannot spread heartworms to another dog since the parasite must pass through a mosquito

Once inside the dog’s body, the larvae grow and develop into adult heartworms, which can cause serious health problems. Heartworm adults are hardy and can live for 5 to 7 years inside a dog’s heart.

Heartworms are more common in areas with a high mosquito population but can occur anywhere. It’s important to have your dog tested for heartworms regularly and to use preventative measures, such as monthly heartworm medication and mosquito control, to reduce the risk of infection.

Symptoms of Heartworms in Dogs

Early Symptoms

Heartworms are a serious condition that can lead to heart failure and death in dogs. Unfortunately, in the early stages of the disease, there may be no visible symptoms. However, as the infection progresses, the following symptoms may occur:

  • Mild persistent cough;
  • Reluctance to exercise;
  • Fatigue after moderate activity;
  • Decreased appetite;
  • Weight loss; and
  • As the disease progresses, dogs may develop a swollen belly due to fluid accumulation.

If your dog exhibits any of these symptoms, it is important to take them to the vet for a heartworm test.

Advanced Symptoms

If left untreated, heartworm disease can progress to the point of causing severe damage to the heart, lungs, and other organs. Advanced symptoms of heartworm disease include:

  • Severe coughing;
  • Shortness of breath;
  • Wheezing;
  • Rapid breathing;
  • Collapse;
  • Pale gums;
  • Dark urine; and
  • In extreme cases, dogs may experience sudden death.

It is important to note that not all dogs with heartworm disease will exhibit all of these symptoms nearly on. Some dogs may only show one or two symptoms, while others may show no symptoms at all. Regular heartworm testing and prevention are the best ways to protect your dog from this serious disease.

Diagnosing Heartworms

Veterinary Examination

The first step in diagnosing heartworms in dogs is a physical examination by a veterinarian. During this examination, the veterinarian will look for signs of heartworm disease, such as a cough, difficulty breathing, fatigue, and weight loss. The veterinarian may also feel for enlarged lymph nodes or an enlarged liver and spleen.

Blood Tests

Blood tests are the most common way to diagnose heartworm disease in dogs. The two most commonly used blood tests are the antigen test and the microfilaria test. 

The antigen test detects the presence of adult female heartworms in the bloodstream. This test is very accurate and can detect heartworms in the early stages of infection. The test only works most effectively 5 months after the dog was bit.

The microfilaria test detects the presence of baby heartworms in the bloodstream. This test is usually used to confirm a positive antigen test.  The best tests for detecting microfilariae are called concentration tests, with the preferred one being the modified Knott’s test.

In some cases, a veterinarian may also recommend additional tests, such as chest X-rays or an ultrasound, to confirm a heartworm diagnosis.

It is important to note that heartworm disease can be difficult to diagnose in its early stages, and some infected dogs may not show any symptoms. Therefore, it is recommended that all dogs be tested for heartworms annually and be treated preventatively.

Treatment Options

There are several treatment options available for dogs with heartworm disease. Treatment can be a long and difficult process, and it is important to work closely with your veterinarian to determine the best course of action for your dog. 

The good news is dogs recover very well from heartworms with proper medication. Just see this happy doggo recover from the disease:

Medication Therapy

Medication therapy is the most common treatment option for heartworm disease. Medication therapy aims to kill the adult heartworms in the dog’s body. This is typically done with a series of injections of a drug called melarsomine

The injections are given to the muscles of the dog’s back, and the dog will be hospitalized for a few days after each injection. In addition to melarsomine injections, the dog will also need to be given a monthly heartworm preventative to kill any new heartworm larvae in the dog’s body.

Surgical Intervention

In some cases, surgical intervention may be necessary to remove adult heartworms from the dog’s body. This is typically done in cases where the heartworms are causing severe damage to the dog’s heart or lungs. 

The surgery involves opening up the dog’s chest and removing the heartworms manually. This is a risky and expensive procedure, and it is typically only done in extreme cases.

It is important to note that prevention is the best way to protect your dog from heartworm disease. Make sure your dog is on a monthly heartworm preventative (6 months for injectables), and get them tested for heartworms annually. 

Prevention Strategies

Heartworm Preventatives

Preventing heartworms is much easier and less expensive than treating an infected dog. There are several heartworm preventatives available, including pills, chewables, and topical treatments. These medications kill the heartworm larvae before they can mature into adult worms. Some of the most commonly used heartworm preventatives are:

  • Ivermectin (Heartgard);
  • Pyrantel (Heartgard);
  • Milbemycin oxime (Interceptor);
  • Selamectin (Revolution); and
  • Moxidectin (ProHeart).

It is important to note that heartworm preventatives should be given year-round, even in colder months. Some owners may be tempted to skip a few months during the winter, but this can put their dog at risk if the weather unexpectedly warms up.

Regular Check-ups

Regular check-ups with a veterinarian are also an important part of heartworm prevention. During these visits, the vet can test for heartworms and discuss the best preventative options for the individual dog.

Dogs should be tested annually for heartworms, even if on preventatives. This is because preventatives are not 100% effective, and a missed dose or a resistant strain of heartworms can still result in an infection.

In addition to heartworm testing, regular check-ups allow the vet to monitor the dog’s overall health and catch any potential issues early on. This can include checking for other parasites, such as fleas and ticks, and discussing any changes in the dog’s behavior or diet.

Owners can significantly reduce the risk of their dog developing heartworm disease by using heartworm preventatives and scheduling regular check-ups with a veterinarian.

Frequently Asked Questions

What are the symptoms of heartworm in dogs?

Heartworm disease in dogs has symptoms such as coughing, difficulty breathing, fatigue, weight loss, and a decreased appetite. In severe cases, dogs may even develop heart failure.

How can heartworm in dogs be diagnosed?

A veterinarian can diagnose heartworm disease in dogs through a blood test. The test detects the presence of heartworm proteins in the dog’s bloodstream. In some cases, imaging tests such as X-rays or ultrasounds may also be used to confirm the diagnosis.

What is the treatment for heartworm in dogs?

Treating heartworm disease in dogs involves a series of injections of a medication called melarsomine. The injections are given over several weeks and are designed to kill the adult heartworms in the dog’s heart and lungs. In some cases, additional medications may be prescribed to manage symptoms and prevent complications.

Is heartworm in dogs curable?

While heartworm disease in dogs can be treated, it is important to note that treatment can be costly and may not always be successful. In addition, treatment can be hard on the dog’s body, and there is always a risk of complications. Prevention is the best way to protect your dog from heartworm disease.

How can heartworm in dogs be prevented?

Heartworm disease in dogs can be prevented through monthly heartworm preventatives. These medications are available in various forms, including pills, topical treatments, and injections. It is important to discuss the best preventative option for your dog with your veterinarian.

What is the prevalence of heartworm in dogs?

Heartworm disease is a common problem in dogs, particularly in areas with a high mosquito population. According to the American Heartworm Society, heartworm disease has been diagnosed in all 50 states in the United States. It is important to have your dog tested for heartworm disease regularly and to take preventative measures to protect them from infection.


Dog owners need to test their pets for heartworms regularly. The disease can be fatal if left untreated, but early detection can lead to successful treatment. There are several ways to check for heartworms, including blood tests and antigen tests. It is important to consult a veterinarian to determine the best testing method for your dog.


Tamsin De La Harpe


Tamsin de la Harpe has nearly two decades of experience with dogs in rescue, training, and behavior modification with fearful and aggressive dogs. She has worked closely with veterinarians and various kennels, building up extensive medical knowledge and an understanding of canine health and physiology. She also spent two years in the animal sciences as a canine nutrition researcher, focusing on longevity and holistic healthcare for our four-legged companions.

Tamsin currently keeps a busy homestead with an assortment of rescue dogs and three Bullmastiffs.

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