Heartgard® Chewables for Heartworm Prevention in Dogs

This monthly chewable helps prevent heartworm disease in dogs. This page explains the large-dog option and how to use it, with US delivery from Canada. You can compare pack sizes, review vet requirements, and explore payment choices without insurance.

What Heartgard Is and How It Works

Heartgard® is a veterinarian-prescribed chew that uses ivermectin to prevent heartworm disease. It works by killing immature heartworm larvae transmitted by mosquitoes before they develop into adults. This medicine is given once a month and is designed for routine prevention, not for treating existing infections.

CanadianInsulin.com is a prescription referral platform. We verify prescriptions with your prescriber when required, and licensed Canadian pharmacies dispense your order.

It is supplied as a palatable chew, making administration straightforward for most dogs. If a combination preventive is recommended, the added deworming agent targets common intestinal roundworms and hookworms. Both options rely on weight-based dosing to match a dog’s size.

Who It’s For

This preventive is labeled for dogs six weeks of age and older. Use the weight band that matches the dog’s current weight. The large size is intended for big dogs; the specific carton marked for Heartgard for dogs 51 100 lbs covers the common large-breed range. It is not for cats or other animals. Dogs should be tested for existing heartworm infection before starting or resuming prevention.

Discuss any history of neurologic disease, recent travel, or concurrent medicines with the veterinarian. Herding breeds can be sensitive to high doses of macrocyclic lactones; the preventive dose used here is much lower, but a veterinarian may advise extra caution in certain situations.

Dosage and Usage

Give the chew once every month, on the same date when possible. Offer it by hand or with a small meal, and watch to be sure the full dose is consumed. Use the carton assigned to Heartgard 51 100 lbs when the dog weighs within that band. If the dog gains or loses weight enough to cross a band, consult a veterinarian before switching sizes.

Administer each dose as a single chew; do not split or combine chews unless directed on the label. Keep a reminder system such as a calendar alert to maintain a consistent monthly schedule. A veterinarian may advise continued dosing during and after mosquito season according to the label.

Strengths and Forms

The chewable comes in weight-based presentations commonly described by weight ranges. Typical options include small (up to 25 lb), medium (26 to 50 lb), and large (51 to 100 lb). Packaging is usually available as 6-dose and 12-dose cartons for routine use. Some cartons show a brown color cue for the large size. Language such as Heartgard 51 100 lb dogs on the outer box helps identify the correct pack. Availability varies by pharmacy and may change over time.

If a broader-spectrum combination preventive is preferred, a product that adds an intestinal dewormer may be selected. Compare details and label directions with the veterinarian before changing products or sizes. See the full range of options in our Pet Medications category.

Missed Dose and Timing

If a scheduled monthly dose is missed, give it as soon as remembered, then return to regular monthly dosing. Do not give two doses on the same day unless a veterinarian specifically instructs it. If the prescriber later recommends Heartgard Plus chewables for dogs 51 to 100 lbs, follow the same once-monthly rhythm unless the prescriber advises otherwise. When multiple doses have been missed, ask a veterinarian about testing before restarting.

Storage and Travel Basics

Store the carton in a dry place at typical room temperatures, away from excess heat and direct sunlight. Keep each chew in its blister until use. As with all medicines, keep out of reach of children and other pets. When you travel, carry the original carton or a copy of the label and a pet’s prescription details. Our pharmacies use temperature-controlled handling when required.

For home storage, avoid bathrooms, vehicles, or other areas with extreme humidity or heat. Do not use chews that are damaged, discolored, or out of date. For travel rules, a veterinarian can provide documentation and timing guidance aligned with the label.

Benefits

This monthly preventive is easy to give and well accepted by many dogs. The chew format avoids topical residue on fur and reduces mess in the home. Weight-based cartons simplify selection for a dog’s size. A consistent schedule can help reduce the risk of heartworm disease in regions where mosquitoes are active. If a combination option is recommended, the added dewormer can address common intestinal worms at the same time.

Side Effects and Safety

• Digestive upset such as vomiting or soft stool
• Reduced appetite
• Lethargy or tiredness
• Itching or mild skin irritation
• Drooling or pawing at the mouth after dosing

Serious adverse reactions are uncommon at preventive doses. Rarely, neurologic signs such as tremors, incoordination, or seizures can occur. Dogs with heavy microfilaria burdens may show signs after dosing; a veterinarian will guide testing and follow-up. Seek urgent veterinary care if a dog shows persistent vomiting, severe lethargy, wobbliness, or other concerning symptoms.

Drug Interactions and Cautions

Tell the veterinarian about all medicines, supplements, and topical treatments the dog receives. Combining macrocyclic lactones with certain drugs that affect P-glycoprotein can increase exposure. Use added caution if the dog takes spinosad, azole antifungals, cyclosporine, or other therapies with known interaction potential. Do not use this preventive to treat active heartworm disease. Follow veterinary guidance if multiple months have been missed or if there has been recent travel to heartworm-endemic areas.

What to Expect Over Time

There is no visible change after each monthly dose. Prevention works by targeting heartworm larvae acquired in the prior month. A veterinarian may recommend periodic testing to confirm ongoing protection. A simple routine of timely dosing, regular exams, and mosquito control can help maintain a dog’s heartworm prevention plan. If administration becomes difficult, a veterinarian can recommend alternative formulations or reminder strategies.

Compare With Alternatives

Some dogs benefit from a broader-spectrum oral preventive. Interceptor Plus combines milbemycin oxime with praziquantel to prevent heartworm and treat several intestinal worms. For owners who prefer an injection given less often, Proheart 6 is a veterinarian-administered option. If evaluating Heartgard for dogs 51 100 alongside these choices, a veterinarian can help match coverage and dosing style to the dog’s needs.

Pricing and Access

Canadian sourcing can offer favorable pricing compared with typical U.S. cash-pay options. Costs vary by pack size and the veterinarian’s prescription. Many large-breed owners choose Heartgard 50 100 lbs in 6-dose or 12-dose cartons. To see current pricing and available pack sizes, check the product page and select the weight band that matches the dog.

To lower out-of-pocket costs further, see current offers on our Promotions page when available. For general tips on buying pet preventives online, read our guide to Affordable Options.

Availability and Substitutions

Supply can vary by size and carton count. If the large-dog chew is temporarily unavailable, the prescriber may recommend an alternative preventive or an interim pack size until the preferred one is restocked. Restock dates are not provided. The veterinarian will decide whether a substitution is appropriate for the dog’s health status and travel plans.

Patient Suitability and Cost-Saving Tips

This preventive suits healthy dogs whose weight falls within a labeled band and who have a current negative heartworm test. It may not be appropriate for dogs with active infection or for those with certain neurologic conditions without close supervision. To stretch the budget, consider a multi-month prescription and consolidate refills. Setting app reminders helps maintain consistent dosing. If a dog also needs intestinal parasite control, ask whether a combination preventive could reduce separate purchases. For broader parasite education, see an overview of Tapeworm Treatment and other New Pet Medications resources.

Questions to Ask Your Clinician

• Start age and testing: when to begin and how often to test
• Correct weight band: how to select and when to adjust
• Giving with food: best way to administer the chew
• Missed doses: what to do after gaps in prevention
• Travel exposure: prevention plan for trips to high-risk areas
• Other preventives: combining flea, tick, and intestinal coverage
• Monitoring: which side effects should prompt a call

Authoritative Sources

• Manufacturer Product Site
• FDA Green Book
• Boehringer Ingelheim Canada

Ready to request the large-dog preventive? Order from CanadianInsulin for prompt, express shipping with US delivery from Canada. Always use exactly as prescribed by a veterinarian.

This information is educational and does not replace a veterinarian’s advice. Review the full label and consult a prescriber for guidance specific to the dog.