Why It Matters:
Heartworm and flea prevention is a crucial part of keeping your dog healthy—especially in Central Texas, where both parasites are a year-round issue. Heartworms are deadly parasites spread by mosquitoes, and without monthly prevention, dogs can suffer lung damage, heart failure, and death. Fleas may seem like just a nuisance, but they can cause severe itching, allergic reactions, skin infections, tapeworms, and widespread infestations in your home.

What Preventatives Do:
Heartworm preventatives kill microscopic larvae (called microfilariae) before they develop into adult worms. Once heartworms mature, prevention no longer works—treatment becomes more complex, risky, and expensive. Flea preventatives work by killing adult fleas and/or stopping eggs and larvae from developing, helping avoid full-blown infestations.

When to Give It:
Heartworm and flea preventatives must be given every 30 days, all year long. In warm regions like Central Texas, skipping even one dose can leave your dog vulnerable. Set reminders using apps like PetDesk or Pawtrack, or mark a calendar to stay on track.

Common Brands:
Your vet can help you choose the best option based on your dog’s needs. For heartworm prevention, oral medications include Heartgard, Interceptor, Sentinel, and Tri-Heart Plus. ProHeart 6 and ProHeart 12 are injectable options that last six and twelve months, respectively. For fleas and ticks, oral products include NexGard, Simparica, and Bravecto, while topical choices include Advantage II, Frontline Plus, and Revolution. Combo products like Simparica Trio and Trifexis protect against both heartworms and fleas.

Affordable Sources:
Low-cost clinics often carry preventatives at discounted rates (see our Resource Page). Online pharmacies such as Chewy and 1800PetMeds may offer deals, and some veterinarians will price-match. Be sure to check for manufacturer rebates, which can significantly reduce the cost.

Heartworm Testing:
Dogs must test negative for heartworms before starting prevention—especially if they’ve missed a dose or are new to your care. Vets typically recommend an annual heartworm test during your dog’s wellness exam.

What Happens Without It:
If a dog becomes infected with heartworms, treatment is long, costly, and dangerous. Left untreated, heartworms can cause permanent damage to the lungs, heart, and arteries—and may be fatal. Fleas can also create widespread infestations that affect other pets and require extensive home treatment.

Missed a Dose?
Give the missed dose as soon as possible. If more than 30 days have passed, call your vet. Your dog may need to be re-tested before restarting prevention to ensure it’s safe.

Puppies & New Dogs:
Puppies can start preventatives as early as 6–8 weeks of age, depending on the product. Your vet will confirm when it’s appropriate and ensure the dose matches your puppy’s current weight. For newly adopted dogs, start prevention after your vet confirms they are heartworm-negative.

What If My Dog Tests Positive for Heartworms?
If your dog tests positive, don’t panic—but treatment must begin quickly. The standard heartworm treatment typically starts with 30 days of oral antibiotics (doxycycline) to weaken the heartworms and prevent complications from bacteria they carry. Your vet may also prescribe a heartworm preventive to stop new infections. After the antibiotic phase, your dog will receive a series of injections of an arsenic-based drug called melarsomine (Immiticide), usually over 2–3 months. During treatment, strict exercise restriction is critical—too much activity can cause heart or lung complications as the worms die. Follow-up testing is done months later to confirm the infection has cleared. The entire process is stressful, expensive (often over $1,000), and can take six months or more.