Heartgard Plus for Dogs: How It Works, Cost & Alternatives

This information is for educational purposes only and does not replace care from your vet. Heartworm prevention should be chosen with your dog's age, weight, travel history, parasite risk, and current medications in mind.

See your vet immediately if your dog has trouble breathing, collapses, has facial swelling, repeated vomiting, tremors, or seems suddenly weak after any medication. If your dog may already have heartworm disease or has gone a long time without prevention, your vet may recommend testing before restarting a product like Heartgard Plus.

Because Heartgard Plus is a prescription medication, your vet should confirm the right dose and timing. Puppies, dogs over 100 pounds, dogs that swallow treats whole, and dogs with a missed-dose history may need extra guidance to use it safely and consistently.

Heartgard Plus is a monthly prescription chew for dogs that combines ivermectin and pyrantel pamoate. Ivermectin prevents heartworm disease by killing the larval stage of Dirofilaria immitis acquired from mosquito bites during the previous month. Pyrantel treats and controls common intestinal worms, especially roundworms and hookworms.

It is labeled for dogs and puppies 6 weeks of age and older. The chew is beef-based and many dogs take it like a treat, but your dog should still be watched to make sure the full dose is chewed and swallowed. The current prescribing information also notes that choking or intestinal obstruction has been reported in some dogs, so dogs that gulp treats may need the chew broken into pieces or given with a small amount of food under your vet's guidance.

Heartgard Plus does not cover fleas, ticks, whipworms, tapeworms, or mites. For many families, that means pairing it with a separate flea and tick product. For others, your vet may suggest a broader-spectrum monthly alternative if you want fewer products to remember.

Heartgard Plus is used first and foremost to help prevent heartworm disease, a serious parasite infection that can damage the heart, lungs, and blood vessels. Heartworm is spread by mosquitoes and has been diagnosed in dogs in all 50 states, which is why many vets recommend prevention year-round rather than only during obvious mosquito season.

The pyrantel portion also treats and controls adult roundworms and adult hookworms listed on the label. That extra intestinal parasite coverage can be especially helpful for puppies, dogs that visit parks or daycare, and dogs that tend to eat stool or investigate contaminated soil.

What it does not do matters too. If your dog also needs flea, tick, or whipworm coverage, Heartgard Plus may still be a good fit, but it may need to be part of a larger parasite plan. Your vet can help match the product to your dog's lifestyle, travel habits, and local parasite pressure.

Heartgard Plus is given by mouth once every 30 days and is dosed by body weight. The labeled chew sizes provide a minimum of 6 mcg/kg ivermectin and 5 mg/kg pyrantel. Dogs over 100 pounds usually need a combination of chew sizes so the total dose matches body weight.

Puppies younger than 7 months can often start prevention without pretesting, but dogs 7 months and older are typically tested before starting or restarting a heartworm preventive. The reason is timing: it takes months after infection for heartworm tests to turn positive, so a dog can look healthy while still carrying developing parasites.

If you miss a dose, give it as soon as you remember and contact your vet, especially if more than 30 days have passed. Your vet may recommend follow-up testing about 6 to 7 months later because larvae acquired during the gap may have matured beyond the stage this medication can eliminate. Try to give each dose on the same calendar date every month to reduce missed-dose risk.

Most dogs tolerate Heartgard Plus well at preventive doses. Mild side effects can include vomiting, diarrhea, decreased appetite, drooling, or low energy after dosing. These signs are often short-lived, but your vet should know if they are severe, repeated, or happen every month.

Rare but more serious concerns include allergic-type reactions, trouble swallowing, choking, or signs that part of the chew was not fully swallowed. If your dog vomits soon after dosing or you think only part of the chew was eaten, call your vet for guidance about whether redosing is appropriate.

Many pet parents ask about ivermectin sensitivity in Collies and related herding breeds with the ABCB1/MDR1 mutation. That concern is real at higher ivermectin doses, but the heartworm-prevention dose in Heartgard Plus is far lower than doses associated with classic ivermectin toxicity. Even so, if your dog has a known mutation, neurologic history, or previous medication sensitivity, it is reasonable to discuss testing and product choice with your vet.

Heartgard Plus has relatively few known interaction problems at labeled preventive doses, and many dogs take it alongside flea and tick preventives, antibiotics, pain medications, and routine long-term prescriptions. Still, your vet should review the full medication list, including supplements, because your dog's overall health matters as much as the label.

The bigger safety issue is not usually a classic drug interaction. It is giving a heartworm preventive to a dog that may already have heartworm infection or restarting prevention after a long lapse without a plan. In those situations, your vet may recommend testing first and may adjust the timing of prevention, retesting, or additional diagnostics.

If your dog is heavily parasitized with intestinal worms, the pyrantel component can occasionally lead to temporary stomach upset as worms die and pass. That is another good reason to tell your vet about diarrhea, weight loss, potbelly appearance, or visible worms before starting any deworming product.

Heartgard Plus is generally considered safe at labeled heartworm-prevention doses even in breeds associated with the ABCB1/MDR1 mutation, but breed history still matters. If your dog is a herding breed or mix, has had neurologic reactions before, or takes multiple medications, your vet may want to review options carefully.

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Heartgard Plus can be given by hand or with a small amount of food, but your dog should be watched to make sure the full chew is eaten and chewed rather than swallowed whole.