ProHeart for Cats: Is the Heartworm Injection Safe?
By Dr. Zubair Khalid, DVM, MS, PhD ·
Is ProHeart 12 for cats safe? The short answer is that ProHeart is not approved for cats in the United States. It is a dog product, and no feline version exists. Cats need a different heartworm preventive, and your veterinarian can help you choose one.
This article is educational and is not a substitute for veterinary diagnosis or treatment.
Quick Answer
- ProHeart 12 and ProHeart 6 are injectable heartworm preventives approved for dogs, not cats. There is no ProHeart injection for cats in the U.S.
- The active drug in ProHeart is moxidectin, which does appear in some cat products, but only in topical formulas made and labeled for felines.
- Heartworm disease in cats is real and can be fatal, and both indoor and outdoor cats can be infected [1].
- Cats are somewhat more resistant to heartworm infection than dogs, and infected cats often carry only 1 to 3 adult worms [1].
- Never give a dog heartworm product to a cat. Ask your veterinarian which feline preventive fits your cat's age, weight, and health.
What Is ProHeart and What Is It Used For?
ProHeart is the brand name for an injectable heartworm preventive that contains moxidectin. In the United States, it is sold in two forms for dogs, one given every six months and one given every twelve months. Both are labeled for dogs only.
That means there is no ProHeart injection for cats. If you search for "ProHeart 6 for cats" or "ProHeart 12 for cats," you will not find an approved feline product. The question "is there ProHeart for cats" has a clear answer: not as an injection.
Moxidectin itself is not foreign to feline medicine. It shows up in topical cat products, often combined with other drugs. One example is a spot-on formula containing fipronil, moxidectin, and praziquantel, which has been evaluated for controlling fleas and common intestinal worms in cats [2][3]. So the drug can be used in cats, but the form, dose, and labeling matter enormously.
Why owners ask about the injection
Injections are appealing. You do not have to remember a monthly dose, and you do not have to wrestle a reluctant cat. For dogs, that convenience is real. For cats, no injectable heartworm preventive is approved, so the convenience argument does not apply.
How Moxidectin Works
Moxidectin belongs to a group of drugs called macrocyclic lactones. These drugs interfere with nerve signaling in parasites, which paralyzes and kills susceptible worms and some external parasites.
In cats, macrocyclic lactones are used topically for parasites such as fleas and certain intestinal worms [2][3]. The drug reaches the parasite, disrupts its nervous system, and the parasite dies.
The same basic mechanism is why these drugs can cause neurological side effects if too much reaches a cat's brain. Cats have a blood-brain barrier that normally keeps many drugs out. A drug transporter called P-glycoprotein helps pump these molecules away from the brain. Some cats have a genetic variant that makes this transporter non-functional. A cat homozygous for the ABCB11930_1931del TC variant has no working P-glycoprotein and faces a higher risk of neurotoxicity from macrocyclic lactones and other drugs that use this transporter [4].
That is one reason dose accuracy matters so much in cats. A dose that is fine for a dog can be dangerous for a cat.
Dosing Basics for Cats
Who decides the dose
Your veterinarian decides. Feline doses are calculated from your cat's body weight, age, and overall health. Never split a dog product or guess at a cat dose. The margin for error is small, and some cats carry the genetic variant that raises toxicity risk [4].
How feline preventives are given
Most heartworm preventives for cats are given monthly. Many are topical spot-on products applied to the skin between the shoulder blades. Some are oral. Your veterinarian will match the product to your cat.
What if you miss a dose
Call your veterinary clinic and ask what to do. Do not double up to catch up. Timing rules differ by product, and your veterinarian knows your cat's history.
A note on testing
Heartworm testing in cats is not straightforward. Diagnosis is one of the harder problems in veterinary medicine because tests have limits, cats may show only brief signs, and some cats die without ever being diagnosed [5]. This is why prevention matters more than detection in cats.
If you want the bigger picture on why prevention is the practical path for felines, see Heartworm Prevention for Cats: Why It's Important and How It Works. For a side-by-side look at both species, read Heartworm Prevention for Dogs and Cats: What Owners Need To Know.
Side Effects: Common and Serious
| Side effect | How common or serious | What to do |
|---|---|---|
| Mild application-site reaction (redness, hair loss, brief itching) with topical products | Uncommon and usually mild | Note it, keep an eye on the spot, call your vet if it worsens |
| Drooling, vomiting, or brief lethargy after an oral dose | Uncommon | Withhold the next dose and call your vet |
| Neurological signs such as dilated pupils, tongue protrusion, weakness, or wobbly walking | Rare but serious | Stop the product and call your veterinarian right away |
| Signs of an allergic reaction (facial swelling, hives, trouble breathing) | Rare but an emergency | Go to an emergency clinic now |
The neurological concern is not theoretical. A young Maine Coon cat developed tongue protrusion, dilated pupils, generalized weakness, and ataxia after a routine application of a macrocyclic lactone product at the labeled dose. Testing found the cat was homozygous for the ABCB11930_1931del TC variant, meaning it had no functional P-glycoprotein. The cat recovered over three months with supportive care [4].
On the other hand, a large review of reported side effects found that topical macrocyclic lactone products, including eprinomectin, showed comparable neurological safety profiles in cats based on post-approval reporting data [6]. In plain terms, serious neurological events are reported rarely across these topical cat products. The risk is real but low, and it is higher in cats with the genetic variant [4].
Who Should Not Take It and Drug Interactions
Because there is no approved ProHeart product for cats, the "who should not take it" question really applies to feline moxidectin products in general.
Cats that should not receive a macrocyclic lactone without careful veterinary review include:
- Cats known to carry the ABCB11930_1931del TC variant or with a known P-glycoprotein deficiency [4]
- Kittens below the minimum age or weight on the specific product label
- Cats that reacted badly to a previous dose of the same drug class
- Cats on other drugs that are also P-glycoprotein substrates, since these can stack up [4]
Tell your veterinarian about every product your cat receives, including flea treatments, dewormers, and anything you bought without a prescription. Cats are often on more than one parasite product at once, and overlapping ingredients are a common and avoidable mistake.
If your cat has intestinal worms and you are sorting out deworming options, Roundworm Treatment for Cats: Safe Dewormers and Prevention covers that ground.
Overdose and When to Call for Help
Signs of macrocyclic lactone overdose in cats include dilated pupils, drooling, unsteady walking, tremors, weakness, and lethargy. These can appear within hours of exposure [4].
If you think your cat received too much of any parasite product, or you are not sure what it got, call your veterinarian or an animal poison control service immediately. Do not wait to see if signs develop. Bring the product packaging with you so the team knows exactly what was given and how much.
If your cat is having trouble breathing, is collapsed, is having seizures, or has facial swelling, treat it as an emergency and go to the nearest emergency clinic now.
Limitations and When to Contact a Veterinarian
No article can tell you what is right for your specific cat. Individual cases need a veterinarian who can examine your cat, weigh it, review its history, and pick a product.
Contact your veterinarian the same day if:
- Your cat shows dilated pupils, drooling, wobbliness, or unusual weakness after any parasite product [4]
- Your cat vomits repeatedly or refuses food after a dose
- You applied a dog product to your cat by mistake
- You are unsure whether a missed dose needs to be repeated
Go to an emergency clinic now if:
- Your cat is struggling to breathe or breathing fast at rest
- Your cat collapses or cannot stand
- Your cat has a seizure
- Your cat's face or throat is swelling
Schedule a routine visit if:
- You want to start heartworm prevention and have not yet
- Your cat is due for its yearly exam and parasite risk review
- You have questions about which product suits an indoor-only cat
Heartworm disease in cats can be fatal, and it is preventable [1]. That is the core reason to have this conversation with your veterinarian instead of skipping it.
Frequently Asked Questions
Is there a ProHeart injection for cats?
No. ProHeart is approved for dogs in the United States, and no feline injectable version exists. If a clinic offers an injectable heartworm preventive for your cat, ask exactly what drug it is and whether it is approved for cats.
Is ProHeart safe for cats?
You cannot give ProHeart to a cat because it is not labeled for felines. Moxidectin, the drug inside ProHeart, is used in some topical cat products, and reported neurological side effects for topical macrocyclic lactones in cats are low in frequency [6]. Rare serious reactions do occur, especially in cats with a specific genetic variant that affects drug handling [4].
Can I just use my dog's heartworm medicine on my cat?
No. Dog products contain doses meant for dogs, and giving them to a cat can cause serious neurological toxicity [4]. Cats need feline-labeled products at feline doses.
Does my indoor cat really need heartworm prevention?
Yes, indoor cats can be infected. Heartworm disease affects both indoor and outdoor cats, and the only way the parasite enters a cat is through a mosquito bite [7][1]. Mosquitoes get indoors.
How do I know if my cat has heartworm disease?
You often cannot tell from signs alone. Diagnosis in cats is difficult because tests have limits, signs can be brief or absent, and some cats die without a confirmed diagnosis [5]. Your veterinarian can discuss testing and, more importantly, prevention. For what happens after a diagnosis, see Heartworm Disease in Cats: Feline Diagnosis and Supportive Care.
Related Articles
- Heartworm Prevention for Dogs and Cats: What Owners Need To Know
- Heartworm Prevention for Cats: Why It's Important and How It Works
- Heartworm Disease in Cats: Feline Diagnosis and Supportive Care
- Roundworm Treatment for Cats: Safe Dewormers and Prevention
- Heartworm Prevention for Dogs: Why It's Essential and How It Works
- Tick Prevention for Cats: What's Safe and Effective?
References
- Heartworm Disease in Cats - Cat Owners. Merck Veterinary Manual.
- Efficacy of a topical formulation containing fipronil, moxidectin and praziquantel (Banni3®) for the control of gastrointestinal helminths of zoonotic importance in naturally infected cats. Brazilian journal of veterinary medicine, 2025.
- Efficacy of a topical formulation combining fipronil, moxidectin, and praziquantel (Banni3) in controlling flea infestation in cats. Frontiers in veterinary science, 2025.
- Inherent P-glycoprotein deficiency and macrocyclic lactone toxicity in an Australian Maine Coon cat homozygous for ABCB11930_1931del TC. JFMS open reports, 2026.
- Evaluation of feline heartworm disease based on gross necropsy, serology, pulmonary histopathology, and radiographic evidence in adult shelter cats in northeastern Alabama. Parasites & vectors, 2024.
- Topically administered macrocyclic lactone products, including eprinomectin, demonstrate comparable neurological safety in cats based on pharmacovigilance data. Journal of the American Veterinary Medical Association, 2026.
- Heartworm in Cats. Cornell University College of Veterinary Medicine.