Year-Round Heartworm Prevention: Why Skipping a Month Is Risky

Keeping up with heartworm prevention year round is one of the simplest things you can do to protect your dog — yet it's also one of the easiest to let slide. A single missed dose can open a window for infection that's far more expensive and stressful to address than a monthly preventative. If you've ever wondered whether it's safe to skip heartworm medication for dogs during cooler months, the short answer is: it isn't worth the gamble.

How Heartworm Disease Works

Heartworm disease is caused by the parasitic worm Dirofilaria immitis, which is transmitted through the bite of an infected mosquito. When a mosquito feeds on your dog, it can deposit microscopic larvae into the skin. Those larvae then migrate through the body over the following months, eventually reaching the heart and pulmonary arteries.

Once mature, heartworms can grow up to 30 cm long and may live for several years inside a host. A heavy worm burden damages the heart, lungs, and blood vessels, leading to serious — and sometimes fatal — complications. The critical thing to understand is that the early stages of infection are completely invisible; dogs can carry developing larvae for months with no outward symptoms at all.

Why Skipping Even One Month Is Risky

Monthly heartworm preventatives work retroactively. Each dose eliminates larvae that entered the body during the previous 30 days or so. When you miss a dose, any larvae deposited in that unprotected window continue to develop unchecked.

By the time you resume treatment, some of those larvae may have matured beyond the stage that monthly products can target. At that point, the developing worms advance toward adulthood — and treating established heartworm disease is a lengthy, costly process that's hard on your dog.

Mosquitoes don't keep a strict calendar. Even during cooler or drier periods, a single unseasonably warm spell can bring them out. That unpredictability is precisely why so many veterinary professionals recommend continuous, uninterrupted protection rather than seasonal dosing.

The Case for Year-Round Protection

Providing heartworm prevention all year round removes the guesswork entirely. You don't need to predict mosquito activity, track seasonal changes, or remember when to start and stop treatment. A consistent monthly schedule keeps your dog defended no matter what the weather does.

Year-round dosing also helps maintain consistent levels of protection against other internal parasites. Many popular heartworm products — such as those in our Heartgard range — also cover common intestinal worms like roundworm and hookworm. That means a single monthly treatment pulls double duty.

There's also a financial argument. Monthly preventatives cost a fraction of what heartworm treatment costs once disease has established. Prevention really is the most budget-friendly strategy.

Choosing the Right Heartworm Medication for Dogs

When selecting heartworm medication for your dog, the most important factors are your pet's weight, age, and any additional parasite protection you need. Some products focus solely on heartworm, while others combine heartworm, flea, tick, and intestinal worm coverage in a single treatment.

Chewable tablets tend to be the most popular option because dogs usually accept them as treats, making compliance easy. Topical spot-on treatments are another reliable choice, especially for dogs that are fussy eaters. You can browse our full selection of flea, tick, and worm products for dogs to compare formats and active ingredients side by side.

Whichever format you choose, consistency matters more than brand. The best heartworm product is the one you'll actually give on time, every single month.

Tips for Staying on Schedule

Life gets busy, and a skipped dose is usually an accident rather than a deliberate choice. Here are a few practical ways to keep your dog's prevention on track:

• Buy in bulk. Purchasing a 6- or 12-month pack means you always have the next dose on hand and reduces the chance of running out.
• Use a calendar or app. Digital reminders remove the need to rely on memory. Many pet-health apps also let you log each dose.
• Store doses visibly. Keep the box near your dog's treats or food so it's in your line of sight around dosing day.
• Pair dosing with another monthly event. Rent day, subscription box delivery, or the first weekend of the month — any regular anchor point works.

If you do realise you've missed a dose, give the next one as soon as possible and then continue on your normal monthly schedule from that date onward.

Frequently Asked Questions

Can I stop heartworm medication during cooler months?

It's not recommended. Mosquito activity can be unpredictable, and even brief warm spells can pose a risk. Maintaining heartworm prevention year round is the safest approach because it eliminates any gaps in protection.

What happens if I miss one month of heartworm medication?

A single missed dose means any larvae transmitted during that period may develop past the stage preventatives can target. Give the missed dose as soon as you remember and continue your regular schedule. If more than two months have passed, it's wise to chat to your vet about whether testing is needed before resuming treatment.

Do heartworm preventatives also protect against other worms?

Many do. Products like those in the Heartgard range also treat and control common intestinal parasites such as roundworm and hookworm. Check the product label or description to see exactly which parasites are covered.

Don't leave your dog's protection to chance. Browse our full range of heartworm, flea, and tick prevention for dogs and lock in year-round cover today.