By Dial A Vet Veterinary Team
Heartworm disease is a serious, mosquito-borne infection. Adult worms live in the heart and pulmonary arteries and can damage the lungs, heart, and vessels over time. Many dogs show few early signs, which is why testing and prevention matter even when pets look well. Related pages: heartworm medicine overview, prevention medications, and ivermectin context for heartworm.
Key takeaways
- Heartworms are transmitted by mosquitoes that carry larval stages of Dirofilaria immitis.
- Early infection can be silent. Later signs may include cough, exercise intolerance, weight loss, and in severe cases collapse.
- Annual (or veterinarian-recommended) antigen testing is part of responsible prevention programs in most regions.
- Treating adult heartworm disease is a multi-step veterinary process. It is not a DIY medication project.
- Year-round preventive medication prescribed by a veterinarian is far safer and cheaper than treating established disease.
How dogs get heartworm
A mosquito bites an infected animal, picks up microfilariae, and later deposits infective larvae into another dog during a blood meal. Those larvae migrate and mature into adults in the pulmonary arteries and right side of the heart over several months. Indoor dogs are not automatically safe; mosquitoes enter homes. Risk varies by climate and travel, but American Heartworm Society guidance commonly emphasizes year-round prevention in many areas.
Signs that need veterinary attention
- Persistent cough
- Tiring quickly on walks or play
- Reduced appetite or gradual weight loss
- Reluctance to exercise
- Swollen belly from fluid (advanced disease)
- Pale gums, fainting, or sudden collapse (emergency)
None of these signs prove heartworm on their own. Many other heart and lung diseases look similar. Testing is required.
Diagnosis themes
Veterinarians commonly use antigen blood tests that detect proteins from adult female worms, sometimes along with tests for microfilariae. Imaging and additional bloodwork help stage disease severity before treatment. Follow your clinic’s testing schedule, especially before starting or restarting preventives after a gap.
Treatment overview (clinic care)
Adulticide therapy for dogs is carefully staged. Clinics may stabilize the patient, address inflammation and clotting risk themes, restrict activity, and use protocol medications under direct veterinary supervision. Some dogs need hospitalization around injections. Activity restriction during treatment is often critical because dying worms can cause dangerous pulmonary complications. Your veterinarian will explain timing, monitoring, and prognosis for your dog’s stage of disease.
Do not give livestock dewormers, leftover preventives, or internet “kill protocols” at home. Wrong products and wrong schedules can be toxic or leave worms untreated.
Prevention
- Use a veterinarian-prescribed preventive on the schedule they recommend (often monthly oral or topical products, or longer-acting injectables given in clinic).
- Keep up with antigen testing as advised.
- Reduce mosquito exposure when practical (screens, standing-water control), knowing this does not replace medication.
- Ask about heartworm risk when traveling to higher-prevalence regions.
FAQ
Can cats get heartworm too?
Yes, though disease patterns differ and cats are not treated the same way as dogs. Ask your veterinarian about feline risk in your area.
Is heartworm contagious dog to dog?
Not directly. Spread requires mosquitoes as the intermediate host.
What if I missed a preventive dose?
Call your veterinarian promptly. They may recommend testing and a safe restart plan rather than guessing at home.
Talk with a vet
Questions about cough, missed preventives, or test results: dialavet.com. Collapse, severe breathing trouble, or known untreated heartworm with sudden decline needs emergency in-person care.
References
- American Heartworm Society. Current canine guidelines themes for prevention, testing, and management.
- Merck Veterinary Manual. Heartworm disease overview.
- AVMA. Heartworm disease public education resources.
Disclaimer: Educational only. Not a substitute for veterinary diagnosis, testing, or treatment. Heartworm care must be individualized by a licensed veterinarian.
