Heartworm Prevention and Treatment in Dogs: Why We Love ProHeart
By Dr. Rachael Kuhn-Siegel, DVM, owner of Prairie Animal Hospital in Brimfield, Illinois, serving pets and families in the Peoria area for 12 years.
Heartworm disease is a serious, potentially fatal infection spread by mosquitoes, and it is far easier to prevent than to treat. Prevention comes down to an annual heartworm test and a preventive given without gaps. For many dogs, the simplest way to stay protected is a ProHeart injection, which your veterinarian gives once and which then covers your dog for either 6 or 12 months. If a dog does become infected, treatment is possible, but it takes months, involves a series of injections and strict rest, and is much harder on your dog (and your wallet) than prevention.
Key takeaways
- Heartworms are spread by mosquitoes, and central Illinois has plenty of them from spring through fall.
- The American Heartworm Society recommends year-round prevention and a heartworm test every year.
- ProHeart 6 protects for 6 months and ProHeart 12 protects for a full year, from a single injection given at your vet’s office.
- ProHeart also treats hookworms, a common intestinal parasite.
- Treating an existing heartworm infection takes several months and requires strict exercise restriction.
What is heartworm disease?
Heartworms (Dirofilaria immitis) are parasitic worms that live in the heart, lungs, and the large blood vessels that connect them. When a mosquito bites an infected animal, it picks up tiny immature worms and can pass them to the next dog it bites. Over roughly six months, those larvae grow into adult worms that can reach up to a foot long.
As the worms grow and multiply, they cause inflammation and lasting damage to the lungs, heart, and blood vessels. That damage is why prevention matters so much: even after a successful treatment, some of the changes to the heart and lungs can be permanent.
Here in the Peoria area, mosquitoes are a fact of life near the Illinois River, in backyards, and anywhere water collects after a summer storm. Indoor dogs are not completely safe either, since it only takes one mosquito slipping through the door.
Signs of heartworm disease in dogs
Early heartworm disease often has no signs at all, which is one of the reasons it is so sneaky. As the infection progresses, you may notice:
- A mild, persistent cough
- Tiring easily on walks or during play
- Decreased appetite and weight loss
- Fast or labored breathing
- A swollen belly from fluid buildup (in advanced disease)
- Sudden collapse, which can happen with a severe, life-threatening complication called caval syndrome
By the time symptoms show up, the disease is usually well established. This is exactly why we test every year rather than waiting for signs.
How heartworm is diagnosed
Heartworm testing is a quick blood test, and many clinics, including ours, can run it in-house during your dog’s wellness visit.
- Antigen test: detects a protein released by adult female heartworms. This is the main screening test.
- Microfilaria test: looks for baby worms circulating in the blood.
If a test comes back positive, we confirm it with a second, different test before starting treatment. From there, chest X-rays, bloodwork, and sometimes an ultrasound of the heart help us understand how much damage has occurred and plan the safest treatment.
Puppies can start preventives without a test before 7 months of age, and should then be tested about six months later and every year after that. Annual testing is still recommended for dogs on prevention, because it catches the rare case where a dose was missed, given late, or did not work as expected.
How heartworm is treated in dogs
Treatment for heartworm disease is effective, but it is a process. Most veterinarians follow the treatment protocol recommended by the American Heartworm Society, which typically includes:
- Exercise restriction from day one. This is the hardest part for many families. As worms die, they can break off and lodge in the lungs, and activity raises that risk. Your dog will need calm, leash-only time outside for the whole treatment period.
- A heartworm preventive to stop new infections and clear young larvae.
- Doxycycline, an antibiotic, for about four weeks. It targets bacteria that live inside heartworms, which weakens the worms and reduces complications.
- Melarsomine injections, the medication that kills adult heartworms. These are usually given as one injection, followed about a month later by two more injections 24 hours apart.
- Steroids such as prednisone, as needed, to reduce inflammation in the lungs.
- Follow-up testing about nine months after the final injection to confirm the worms are gone.
All told, treatment takes several months from start to finish. It is very doable, and we will walk you through every step, but it is not something we would ever wish on a dog that could have been protected.
Some people ask about the “slow kill” approach, which uses a preventive alone over a long period. The American Heartworm Society does not recommend it as a routine option, because adult worms keep damaging the heart and lungs for as long as they are alive.
Heartworm prevention: your options
Every approved heartworm preventive works well when it is given correctly and on time. The real-world challenge is consistency. Monthly chews and topicals are easy to forget, especially in a busy household, during a move, or in the winter months when heartworm feels like a summer problem.
Your main options are:
- Monthly chewable tablets, many of which also cover intestinal worms, and some of which also cover fleas and ticks
- Monthly topical products applied to the skin
- ProHeart injections, given by your veterinarian every 6 or 12 months
Why we love ProHeart
ProHeart is an injectable heartworm preventive made by Zoetis. It contains moxidectin in an extended-release form that slowly protects your dog over time. There are two versions:
- ProHeart 6 protects for 6 months and is approved for dogs 6 months of age and older.
- ProHeart 12 protects for 12 months and is approved for dogs 12 months of age and older.
Here is why ProHeart is a favorite in our practice:
- No missed doses. Once your dog has the injection, protection keeps working whether or not anyone remembers the first of the month.
- One less thing to manage at home. No chasing a dog with a pill, no hiding tablets in cheese, and no wondering whether your dog spit it out behind the couch.
- Hookworm treatment included. ProHeart also treats hookworm infections, a common intestinal parasite that can also affect people.
- It fits naturally into your dog’s wellness visit. For many dogs, ProHeart 12 lines up neatly with their yearly exam, vaccines, and heartworm test, so everything happens in one appointment.
- Given by your veterinary team. Because we give the injection ourselves, we know your dog was dosed correctly for their weight.
Is ProHeart safe?
ProHeart has a long track record and is well tolerated by most dogs. As with any medication or vaccine, side effects can occur. The most common are mild, such as brief lethargy, vomiting, or tenderness at the injection site. Allergic reactions are uncommon but can be serious, so we ask you to watch your dog after the injection and call us right away if you notice facial swelling, hives, vomiting, weakness, or trouble breathing.
Before giving ProHeart, we will:
- Run a heartworm test to make sure your dog is negative
- Weigh your dog to dose accurately
- Do a physical exam, since ProHeart is not recommended for dogs that are sick, debilitated, or underweight
- Talk through your dog’s history, including any previous reactions to vaccines or medications
We are always happy to talk about whether ProHeart, a monthly preventive, or a combination with flea and tick protection makes the most sense for your dog and your lifestyle.
Why year-round prevention matters
It is tempting to stop heartworm prevention in winter, and Illinois winters certainly feel mosquito-free. The American Heartworm Society still recommends year-round prevention for several reasons: mosquito seasons are unpredictable, warm spells happen, gaps in coverage are easy to forget to restart, and many preventives also protect against intestinal parasites that do not take the winter off. A 12-month injection takes the seasonal guesswork out of the picture entirely.
Frequently asked questions
How often does my dog need a heartworm test?
The American Heartworm Society recommends a heartworm test every year, even for dogs that stay on prevention year-round.
How long does ProHeart last?
ProHeart 6 protects for 6 months, and ProHeart 12 protects for 12 months from a single injection.
Can puppies get ProHeart?
ProHeart 6 is approved for dogs 6 months and older, and ProHeart 12 is approved for dogs 12 months and older. Younger puppies can start on a monthly preventive and switch to ProHeart once they are old enough.
Can my dog get ProHeart if they have heartworms?
No. Dogs must test negative for heartworm before receiving ProHeart. If your dog tests positive, we will build a treatment plan first.
Does ProHeart protect against fleas and ticks?
No. ProHeart prevents heartworm disease and treats hookworms, but it does not cover fleas or ticks. Many dogs pair it with a separate flea and tick product, and we can help you choose one.
Is heartworm treatment painful for my dog?
The melarsomine injections are given deep in the back muscles and can cause soreness for a few days. We use pain medication as needed and do everything we can to keep your dog comfortable throughout treatment.
Can cats get heartworm?
Yes, although it is less common and looks very different in cats. There is no approved treatment for heartworm in cats, which makes prevention especially important for them. Ask us about feline heartworm prevention at your cat’s next visit.
Ready to make heartworm prevention one less thing to remember? Call us or request an appointment, and ask about ProHeart at your dog’s next visit.