A Comprehensive Guide to Understanding Heartworm in Pets

Estimated Reading Time: 3 min | Last Updated: April 30th, 2024

Heartworm in pets is a serious and potentially fatal condition affecting pets across the globe. It’s caused by a parasitic worm called Dirofilaria immitis, which is transmitted through the bite of an infected mosquito. As a pet owner, understanding the risks, prevention methods, and treatment options available for heartworm disease is crucial for your pet’s health and well-being. Here, we’ve compiled a comprehensive guide from the perspective of a general practice veterinary surgery to help you navigate the complexities of heartworms in pets.

What Are Heartworms? 

Heartworms are long, thin worms that can grow up to 12 inches in length. They live in the heart, lungs, and associated blood vessels of infected animals, causing severe lung disease, heart failure, and damage to other organs in the body. Heartworm disease affects dogs, cats, and ferrets, but can also be found in other mammals, including wolves, coyotes, and, in rare instances, humans. 

How Do Pets Get Heartworms? 

The lifecycle of heartworms begins when a mosquito bites an infected animal and ingests the microfilariae (baby worms) circulating in their blood. These microfilariae mature into infectious larvae within the mosquito. When this mosquito bites another pet, the larvae are transmitted and eventually mature into adult heartworms in the host’s body. 

Cat and Dog laying on grass

Signs and Symptoms 


Heartworm in dogs manifests through various signs and symptoms, ranging from mild to severe as the condition progresses. Initially, dogs may exhibit a mild, persistent cough that doesn’t seem to go away. This is often coupled with a noticeable reluctance to exercise, even for activities they previously enjoyed. After engaging in moderate activity, affected dogs may show signs of fatigue much more quickly than usual. As the condition worsens, dogs might experience a decreased appetite, leading to significant weight loss over time. In advanced cases of heartworm, dogs can suffer from a swollen belly, a result of excess fluid accumulation. These symptoms highlight the serious impact heartworm can have on a dog’s health and well-being.


Heartworm in cats can present with signs and symptoms that may initially be mistaken for other conditions. Cats may experience asthma-like attacks, which are sudden and distressing episodes of difficulty breathing. These episodes may be accompanied by periodic vomiting, adding to the concern for their health. A lack of appetite is also a common symptom, leading to noticeable weight loss over time. Alarmingly, heartworm in cats can be particularly insidious, as it may not reveal itself through noticeable symptoms until it’s too late. In some cases, the first sign of heartworm disease could be a sudden collapse or even death, underscoring the importance of preventive measures and early detection in feline health care.

Early detection is critical for effective treatment and a positive outcome. General practice veterinarians use a combination of tests to diagnose heartworm disease, including blood tests to detect the presence of heartworm proteins (antigens) and microfilariae, X-rays, and ultrasound to assess heart and lung damage. 

Heartworm treatment infographic

Heartworm Prevention 

Preventive measures are the most effective way to protect your pet from heartworm disease. Monthly preventatives are available in various forms, including oral tablets, topical liquids, and injectable products. Year-round prevention is recommended, as it not only protects against heartworms but also against other parasites. Heartworm preventatives can include Nexgard Spectra, Bravecto or heartworm injections.

Treatment for Heartworm 

Treatment for heartworm disease can be complex and carries significant risks, particularly for dogs. The goal is to kill both adult and immature worms with adulticide and microfilaricide medications. Treatment may also include antibiotics, anti-inflammatory drugs, and, in severe cases, surgery.  

The Role of General Practice Veterinary Surgery 

Our Hope Island veterinarians play a crucial role in the management of heartworm disease. They are the first line of defence in diagnosing, prescribing preventative medication, and managing treatment protocols for infected pets. Additionally, they provide valuable education to pet owners about the importance of prevention and early detection. 

Heartworm disease is a severe and life-threatening condition that can affect your beloved pets. However, with proper preventive measures, early detection, and treatment, you can protect your furry friends from this dangerous parasite. Remember, the key to combating heartworm disease is a strong partnership with your general practice veterinarian, who can guide you through the best preventive practices and treatment options for your pets. 

Stay proactive in your pet’s health by scheduling regular check-ups, adhering to a preventative medication schedule, and staying informed about the risks and signs of heartworm disease. Together, we can ensure that your pets lead healthy, happy lives free from the threat of heartworms. 

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