Many pet owners assume that heartworm prevention is something they only need to think about during the warmer months. After all, if mosquitoes are the culprits, surely winter brings a break from the threat—right? Not exactly. For National Heartworm Awareness Month at Madera Veterinary Hospital, we want to set the record straight: heartworm prevention is a year-round responsibility, no matter where you live. Staying consistent every month of the year is necessary to protect cats and dogs from heartworm disease.

The Myth of “Mosquito Season”

Heartworm disease and mosquitos have been reported in all 50 states. While mosquitoes are certainly more active in warmer temperatures, certain species are not entirely dormant during colder months—especially in areas with milder winters. Indoor environments and unexpected warm spells can allow mosquitoes to thrive even when you least expect it. In fact, in many regions, mosquito season lasts longer than it used to. That means the window of risk for heartworm transmission is open far beyond the traditional summer months.

Heartworm Prevention Isn’t Retroactive

One of the biggest misconceptions about heartworm medication is that it acts like a vaccine. It doesn’t. Instead, monthly preventives eliminate heartworm larvae that may have been transmitted in the previous 30 days. This means if you skip even one dose, your pet could be unprotected and infected by the time you restart prevention. Because of this delay, missing doses during cold months can lead to undetected infections that begin silently and worsen over time.

Why Year-Round Heartworm Prevention Works Best for Pets

There are several strong reasons to maintain prevention all year long.

• Mosquitoes are unpredictable. They don’t follow the calendar.
• Prevention is a monthly habit. Keeping it consistent avoids gaps in protection.
• Missed doses increase risk. One lapse can expose your pet to infection.
• Many pets do not show heartworm symptoms until heartworm disease has progressed.

It can be easy to forget a dose, especially during busy months or when mosquitoes seem scarce. Staying consistent now is a small effort that saves your pet from a much larger problem down the road. Pet owners can keep heartworm prevention consistent by: 

• Setting recurring calendar reminders or phone alarms
• Syncing parasite prevention with another monthly task like paying a bill
• Asking your veterinarian about long-acting injectables (for dogs)
• Signing up for automatic refills or delivery programs

Why Does Your Pet Need Annual Heartworm Testing?

Even if your pet has never missed a dose of parasite prevention, annual heartworm testing is a must. Preventatives are highly effective, but they’re not infallible—no product offers a 100% guarantee. Missed or delayed doses, pets who spit out or vomit pills without notice, and rare cases of drug resistance are all reasons infections can still occur.

Annual heartworm testing acts as your safety net, confirming that your pet is free of infection before continuing with prevention. If heartworms are present, continuing medication will have no effect or, in some cases, can actually cause serious complications.

A standard heartworm test is simple and quick—just a small blood sample and a few minutes of analysis during an annual wellness visit. If positive, your vet may follow up with additional diagnostics to determine the severity of the infection and plan appropriate care.

Heartworm Prevention in Tucson Isn’t Seasonal—It’s Lifesaving

The idea that heartworm prevention is only needed part of the year is outdated—and risky. With mosquitoes adapting and prevention working on a monthly basis, year-round protection is the only reliable choice. Madera Veterinary Hospital in Tucson, AZ works with pet owners to build a simple, consistent heartworm prevention plan that works all year long. Don’t let your guard down during the off-season. Book an appointment today to schedule your pet’s heartworm test and make sure they’re protected every month of the year.