Heartworm Disease
A serious, largely preventable parasitic disease affecting the heart and lungs.
What is Heartworm Disease?
Heartworms are transmitted by mosquito bites. Once inside the dog, larvae mature over 6 months into adult worms living in the heart and pulmonary arteries. Prevention is inexpensive and safe; treatment of established infection is expensive, prolonged, and carries real risks.
Common signs and symptoms
Signs vary between dogs and can be subtle at first. Watch for the following, especially if several appear together or persist for more than a few days:
- Early: no signs at all
- Persistent soft cough
- Reduced exercise tolerance
- Weight loss and reduced appetite
- Distended abdomen (advanced disease)
- Sudden collapse (caval syndrome, emergency)
Risk factors
Certain dogs are more predisposed. Understanding risk helps you screen earlier and act sooner.
- Any unprotected dog in a mosquito-endemic area
- Now present in all 50 US states and much of Europe
- Highest risk in warm, humid climates
When to see a vet
Use this as general triage guidance, not a substitute for veterinary advice.
- Book a routine appointment if: annual heartworm testing plus year-round prevention for every dog. Don't skip prevention seasonally — climate change has extended mosquito seasons.
- Seek urgent care if: severe cough with collapse in a heartworm-positive dog.
Diagnosis and management
Prevention with monthly oral, topical, or injectable products is highly effective. Treatment of confirmed heartworm disease follows the American Heartworm Society protocol: doxycycline, then a series of melarsomine injections, with strict exercise restriction throughout.