Heartworm disease is spread by mosquitoes and is far easier to prevent than to treat. Most veterinarians recommend year-round prevention for dogs, and many recommend it for cats too, depending on where you live. This guide explains the common forms of prevention and how to compare what you pay, without replacing your vet's advice.
The main forms of prevention
Monthly chewables and topicals are the most common option. A chewable is given by mouth once a month. A topical is applied to the skin. Both are dosed by your pet's weight.
Some veterinary clinics also offer a long-acting injection for dogs, given by a vet every six or twelve months. Ask your vet whether it suits your dog, since it has to be given in the clinic.
A test comes first
Dogs are normally tested for heartworm before starting or restarting prevention. Giving prevention to a dog that already has heartworms can cause problems, which is why vets ask for a recent test. Your vet will tell you how often to retest.
Why weight matters
Every product comes in weight bands. A dose that is right for a 20-pound dog is not right for a 60-pound dog. If your pet is close to the edge of a band, or still growing, ask your vet which size to buy.
How to compare prices
Compare cost per month, not the price on the box. A six-month or twelve-month pack looks expensive until you divide it by the number of months. Check the same product, in the same weight band, across several pharmacies. Our heartworm comparison does this calculation for you.
Also check whether the pharmacy offers an autoship discount and whether it needs a prescription. Heartworm prevention requires a prescription in the US, so a licensed pharmacy will verify it with your vet.
The bottom line
Test first, match the product to your pet's weight, and compare cost per month across licensed pharmacies. Your vet decides which product is right; the comparison only decides where to buy it.