Year-Round Heartworm Protection for Dogs: Why Vets Recommend Heartgard Plus Every Month

Heartworm disease is a silent but deadly threat to dogs. A single mosquito bite can infect your pet, and treatment is painful, risky, and expensive. Many owners assume heartworm is only a seasonal problem, but this misconception leaves dogs vulnerable. According to the latest veterinary guidelines and the FDA, dogs need heartworm pills every month of the year to stay protected. Year-round prevention is the only safe approach recommended by veterinarians.

This article explains why continuous protection matters, how heartworm spreads, and the best practices to keep your dog safe, healthy, and free from this dangerous parasite.

Why Year-Round Heartworm Prevention Matters?

Heartworm disease affects dogs in all 50 U.S. states. No state in the U.S. was heartworm-free in 2019, according to the American Heartworm Society survey. This nationwide presence makes year-round prevention essential for every dog owner. The statistics paint a concerning picture. 

According to a study published by the National Library of Medicine, only about one in three dogs in the U.S. receives heartworm prevention each year. This leaves millions of pets exposed to a deadly but preventable disease.

Monthly heartworm preventatives work by killing heartworm larvae that have entered your dog’s system in the previous 30-45 days. This retroactive action means any gap in prevention could allow larvae to mature into adult heartworms. Once established, these parasites can cause severe heart and lung damage.

How Are Heartworms Transmitted?

Dogs get heartworm disease through the bite of an infected mosquito. The mosquito picks up microscopic heartworm larvae, called microfilariae, when it feeds on a dog that already has heartworms. Inside the mosquito, these larvae develop into an infective stage. When the mosquito bites another dog, it deposits the larvae into the dog’s skin and bloodstream. Over time, the larvae travel through the body and grow into adult worms, mainly settling in the heart, lungs, and nearby blood vessels. 

Dogs cannot give heartworm to each other directly. Transmission only happens through mosquitoes. This means even a single mosquito bite can start an infection. Because mosquitoes can appear unexpectedly and survive in many climates, dogs remain at risk throughout the year. Understanding this transmission cycle shows why year-round heartworm prevention is essential.

Dispelling the Myth of the Heartworm Season

The Texas A&M Veterinary Medical Diagnostic Laboratory explains that many people believe dogs only need heartworm prevention in the summer. However, mosquitoes that spread heartworm can be active beyond just warm months. Mosquito eggs can survive harsh weather and hatch when conditions improve. Also, mosquitoes can come indoors where pets live. Because of this, heartworm can be a risk year-round, not just during one season. This means giving heartworm prevention medicines all year is the safest way to protect dogs. Relying only on “heartworm season” leaves pets vulnerable when mosquitoes are active outside typical months.

Risks of Seasonal Prevention

Stopping heartworm prevention during certain months can put dogs at serious risk. A study in the Mississippi Delta found that most dogs with heartworm had missed doses or stopped treatment. In fact, over 90% of infected dogs had gaps in their prevention routine. Some owners skipped several months, while others only gave the medicine part of the year. Even short breaks can leave dogs unprotected, because heartworm can spread when mosquitoes appear earlier or stay active longer than expected. The research showed that most infections happened because of missed or delayed doses and not because the medicine didn’t work. Year-round prevention is the safest way to keep your dog protected.

Climate Change and Microclimates

Climate change has expanded heartworm distribution patterns and extended transmission seasons. Rising temperatures allow mosquitoes to survive in previously inhospitable regions. Areas that once experienced reliable mosquito-free periods now face year-round transmission risks.

Urban heat islands create microclimates that support extended mosquito activity. Downtown areas, shopping centers, and residential developments maintain warmer temperatures than surrounding rural areas. These heat pockets can support mosquito populations well into the winter months.

Indoor overwintering represents a significant overlooked risk factor. Mosquitoes can complete their lifecycle in heated buildings, greenhouses, and other protected environments. Basements with standing water, indoor plants, and pet water bowls can support mosquito breeding throughout winter.

How to Safely Administer Monthly Heartworm Pills?

Proper administration of heartworm preventatives ensures maximum protection for your dog. Most monthly heartworm medications come in flavored tablets that dogs readily accept as treats. However, proper dosing and timing remain critical for effectiveness.

Starting Age and Dosage Guidelines

Puppies can begin heartworm prevention as early as 6-8 weeks of age. Most veterinarians recommend starting prevention immediately after the first puppy examination. Early protection prevents infection during the vulnerable juvenile period when the immune system is still developing.

Adult dogs require testing before starting prevention. Heartworm antigen tests detect adult female heartworms in the bloodstream. Giving preventatives to dogs with existing heartworm infections can cause severe reactions. Pre-treatment testing ensures safe medication administration. Always consult your vet for guidance on missed doses.

Veterinary Testing and Prescription Requirements

Heartworm preventatives require veterinary prescriptions in the United States. This requirement ensures appropriate medication selection and proper monitoring for adverse reactions. Annual veterinary examinations typically include heartworm testing and prescription renewal.

Antigen testing detects adult female heartworms in circulating blood. These tests can identify infections approximately 5-7 months after initial exposure. Earlier detection requires specialized testing that most veterinary clinics don’t routinely perform.

Microfilariae testing identifies baby heartworms in blood samples. This testing complements antigen testing and helps determine infection severity. However, not all heartworm infections produce detectable microfilariae, making antigen testing the primary diagnostic method.

Annual testing ensures early detection of breakthrough infections. Even dogs receiving regular prevention can occasionally develop heartworm infections due to medication failures, missed doses, or resistance issues. Early detection allows for prompt treatment before severe complications develop.

Regional Heartworm Risk and Prevention Timeline

Heartworm risk is highest in the warm, humid Southeast, especially in Mississippi, Louisiana, South Carolina, Arkansas, and Alabama. Mosquitoes thrive here year-round, keeping transmission active. 

Northern states see fewer cases, but the risk remains due to travel and rescue dog transport from high-risk areas. Even in cooler climates, indoor mosquitoes can survive winter and spread heartworm. Seasonal peaks may vary, but the threat never fully disappears. 

For that reason, veterinarians recommend year-round prevention. Consistent protection is the safest way to keep your dog heartworm-free, no matter where you live.

Common Questions Answered (FAQs)

What months do dogs need heartworm pills? 

Dogs need heartworm pills every month of the year. There is no safe seasonal approach to heartworm prevention. Monthly preventatives work retroactively, killing larvae that infected your dog in the previous month. Any gap in prevention creates vulnerability to heartworm infection.

What months do dogs need flea and tick medicine? 

In the USA, veterinarians recommend that dogs receive flea protection year-round and tick protection for 9–12 months. Many owners recall 8–10 months. Follow your vet’s guidance for timing and product selection to ensure safe, effective protection.

How long can a dog go without heartworm pills? 

The time a dog can safely go without heartworm pills depends on factors like missed doses and local risk. Only a veterinarian can advise on the right steps, testing, and prevention schedule for your dog’s specific situation.

What is heartworm season for dogs? 

There is no safe “heartworm season” approach to prevention. All major veterinary authorities recommend year-round prevention due to climate variability, indoor mosquito survival, and travel risks. The concept of heartworm season is a dangerous misconception that has led to countless preventable infections.

Can heartworm preventatives be given year-round safely? 

Yes, monthly heartworm preventatives are designed for continuous year-round use. These medications have excellent safety profiles when used according to label directions. The benefits of continuous protection far outweigh any minimal risks associated with long-term use.

Are there natural alternatives to heartworm prevention? 

No natural remedies provide reliable heartworm prevention. Only FDA-approved heartworm preventatives have proven efficacy against heartworm infections [1]. Natural products may offer some mosquito repellent effects, but cannot replace prescription prevention medications [1].

Conclusion: Ensuring Lifelong Protection

Heartworm prevention is a lifelong commitment. Giving your dog a pill every month is the safest way to stay protected. Seasonal gaps are risky because mosquitoes can appear anytime, even indoors. One bite is enough to start an infection.

Monthly prevention is simple, safe, and far less costly than treatment. Annual testing and regular veterinary checkups keep your dog’s prevention plan effective. Consistent prevention also reduces the heartworm risk for other dogs in your community.

DoctorSolve works with licensed Canadian pharmacies to provide access to trusted heartworm prevention, including Heartgard. American pet owners can order genuine, veterinarian-approved medication at affordable Canadian prices.

• Buy Heartgard Plus Chewable Blue (for dogs 1–25 lbs)
• Buy Heartgard Plus Chewable Green (for dogs 25–50 lbs)
• Buy Heartgard Plus Chewable Brown (for dogs over 50 lbs)

Each product is sourced from licensed Canadian pharmacies and meets the same safety and quality standards used by veterinarians. Ordering through DoctorSolve helps American pet owners save while keeping their dogs protected from heartworm disease year-round.

References

• FDA.gov. (2023). An Ounce of Prevention is Worth a Pound of Cure: Protect Your Pet from Heartworms Year-Round
• American Heartworm Society. (2025). Heartworm in Dogs
• American Heartworm Society. (2020). The States of Heartworm Incidence
• National Library of Medicine. (2018). Increasing incidence of Dirofilaria immitis in dogs in USA with focus on the southeast region 2013-2016
• CDC.gov. (2019). Dirofilariasis
• Avma.org. (2025). Heartworm disease
• Texas A&M Veterinary Medical Diagnostic Laboratory. (2024). Not every worm follows the rules: Three misconceptions about heartworm disease.
• National Library of Medicine. (2017). Investigating management choices for canine heartworm disease in northern Mississippi
• National Library of Medicine. (2021). Infection risk varies within urbanized landscapes: the case of coyotes and heartworm
• National Library of Medicine. (2018). The safety-net story about macrocyclic lactone heartworm preventives: a review, an update, and recommendations
• FDA.gov. (1998). FREEDOM OF INFORMATION SUMMARY
• FDA.gov. (2018). FREEDOM OF INFORMATION SUMMARY
• FDA.gov. (2022). Keep the Worms Out of Your Pet’s Heart! The Facts about Heartworm Disease
• American Heartworm Society. (2014). Prevention, Diagnosis, and Management of Heartworm(Dirofilaria immitis) Infection in Dogs
• National Library of Medicine. (2021). Optimizing heartworm diagnosis in dogs using multiple test combinations
• National Library of Medicine. (2024). Evaluation of diagnostic techniques for early detection of heartworm in experimentally infected dogs: identification of Dirofilaria immitis-derived microRNA in the initial 28 weeks post-inoculation
• American Heartworm Society. (2019). No State is Heartworm Free
• National Library of Medicine. (2020). Flea and tick treatment satisfaction, preference, and adherence of dog owners in the United States, United Kingdom, and Australia who treated their dog with fluralaner