Revolution For Dog and Cat Heartworm Preventive

Revolution is a monthly heartworm preventive for cats and dogs that also both controls and prevents fleas.’s Dr. James W. Randolph recommends this Pfizer Animal Health medication for many of his canine and feline patients in his own private practice in Long Beach, MS.

Heartworm infestation can lead to heart failure and death
Heartworm infestation can lead to heart failure and death

Heartworm disease is a life-threatening parasitic infestation for both species. However, it presents as a very different syndrome in dogs compared to cats.

In dogs the disease is fairly gradual, and from the initial time of infestation to death may be a year or more.

In cats, however, sudden death is one of the most commonly observed syndromes associated with heartworm disease.

That’s because Dirofilaria immitis, the scientific name of the heartworm parasite, is a usual parasite in the dog but an aberrant parasite in the cat. So, dogs tolerate the parasite fairly well and damage to the heart, lungs and pulmonary arteries progresses slowly but persistently.

In your kitty, however, violent reactions occur immediately in the pre-adult larval stages of heartworm infestation. By the time as few as 1-3 heartworms become adults, the reactions may progress to acute pulmonary edema (lungs filling with fluid) and death. Other, more tolerant cats, may suffer months or years of asthma-like signs and sub-lethal pulmonary edema, as well as a multitude of other possible problems.

Humans, too, may become infected with D. immitis. As another aberrant host, heartworms may do bizarre things in people, such as infect the eye, brain and abdominal organs. Fortunately, infestation of people is a rarity, and people don’t need to be on heartworm preventives.

I can’t overemphasize: All cats need to be on heartworm preventive! Let’s look at it from a risk/benefit standpoint.

On the risk side you have a disease (1) that will almost assuredly kill your cat, (2) for which there is no approved or effective treatment and, (3) which, even if it isn’t fatal, could easily cost you thousands of dollars and your cat untold suffering treating non-lethal episodes.

On the benefit side, (1) it’s incredibly easy to prevent with monthly medication, (2) the monthly medication is inexpensive, and, (3) Revolution also provides both flea control and flea prevention!

In the modern vernacular, it’s a no-brainer!

What is flea control and what is flea prevention?

Revolution provides flea control by killing adult fleas. Alone, that would be pretty good.

But, flea prevention involves killing the egg and larva stages of the pre-adult flea, so those will never be able to mature and become adult, biting fleas. The more fleas killed in this stage the better, as it’s the bite of the flea that hurts and causes anemia from blood loss.

To summarize, Revolution is a monthly medication from Pfizer Animal Health, approved for use in dogs and cats for prevention of Dirofilaria immitis heartworm infestation, killing adult fleas, flea eggs and flea larvae. It is colorless, odorless easy to use.

Contact your pet’s doctor to find out whether it’s right for your dog or cat.

Default image
Dr. Randolph
Articles: 949


  1. Dr. Randolph, have you heard of any cases of Revolution causing cancer in cats? My 6 yr old Siamese was perfectly healthy at her checkup in March. I started using Revolution in April and she started limping in July. By the time my veterinarian determined it was cancer 2 months in September she was gone. I can’t help but wondering if the Revolution didn’t cause the cancer.

    • Kristi, I’m so sorry to hear about losing your kitty. I know of no suspected cases of Revolution being implicated in cancer. Further, the timeline doesn’t fit. Few cancers can go from induction to tumor growth to death in a time as short as April to September. Even really aggressive carcinogens (in general) take much longer than that. Indeed, cancerous tumors in six-year-old cats are not something we see often. Billions of doses or Revolution have been used and if there were carcinogenic factors involved there would be an outcry by now. By the way, I use Revolution on my own dog every month. Was the tumor biopsied either before or immediately after she passed away? Knowing the cell type of the tumor would certainly be important information to try to determine an underlying cause. Write back if you know. Again, we are very sorry for your loss, Dr. Randolph.

  2. I have recently put Revolution on my 6yr old cat, as I do every month and the next day his skin was burnt and the fur has gone around that area. Two weeks later, his skin is still blistered and scabby and although it doesn’t seem to worry him, it looks unsightly. I have heard from friends they have had similar reactions from their cats. Have they changed the ingredients? Do you know of other cases? My friends say their cat’s fur has never grown back over that spot. Is there anything I can put on it? Thank you, Audrey

    • Audrey, this is a problem that occurs in some cases. I have seen it more frequently in cats than in dogs, but I don’t know what the underlying cause is. The percentage of cats to whom this happens is extremely low. There are two approaches I take when this occurs. One, I ask the pet owner to alternate sites, putting the Revolution about an inch lower on the back this month, and a little forward of the original site next month. Doing so allows the skin to “rest” and heal where the inflammatory process is seen. Second, if this fails to give satisfactory results, I sometimes change the patient’s heartworm preventive to a totally different product. There is nothing available that is as easy and effective as Revolution for both heartworm preventive and flea control and flea prevention, but for that small portion of the cat population that doesn’t tolerate Revolution, change is the only other choice. One other thing to determine: Is your Revolution genuine Pfizer product? Contact Pfizer Animal Health with the lot number to be sure. I have seen some Australian Web sites selling some truly disreputable products. Just because the package says it’s Revolution doesn’t mean it is! Click here to read more. And here to read what the US FDA has to say.

  3. Hi again Dr. Randolph! I was thinking more skin mites. I have two (three year old) brother dogs – one 90 pounds and one 60. The larger dog is now heartworm-free, after one year of heartworm treatments. The smaller dog is still positive and always has more skin issues than his brother. Same skin issues, but the smaller dog’s escalates to needing antibiotics while the larger dog can shake it off with massages and oils. They were born of brother/sister parents (wild dogs) and I suspect the smaller one has a compromised immune system. Of the litter of seven, only the three black and white tuxedo dogs have any skin issues. The smaller dog always has more skin issues, that looks like mange but no mites are ever found. Since Revolution is also for sarcoptic mange, I was kind of thinking it might also help my skin-issue dog. And yes, we have ruled out food allergies, fleas (none) – this is a seasonal (summer heat) skin outbreak that happens each summer. Thank you, again, for your time and help.

  4. Dr. Randolph – Thank you for providing such wonderful information! My question: I have a heartworm-positive dog (diagnosed 1 year ago, has had two doxycycline treatments) who has been on Heartgard for one year. He is currently on Program for fleas, but I would like to switch him to Revolution (for the added mite protection). Since Revolution is not that effective in killing heartworm microfilaria, can I give both Heartgard and Revolution together with no adverse effects? Thanks again.

    • Julie, please read There you will see that killing microfilaria is not a feat without some danger. However, as your dog has been on Heartgard for a year, the likelkihood of having any microfilaria left is very small. Heartgard is an excellent microfilaricide. What I don’t understand is what kind of mites you’re trying to prevent. Revolution is pretty good at killing ear mites, but dogs old enough to have heartworms rarely have ear mites. You can read about them here: . If your dog is having ear problems he needs a thorough examination, combined with a low-power smear of the ear discharge for ear mites and a high-power examination of a stained slide for infectious organisms such as bacteria and yeast. If you’re interested in controlling other kinds of mites you should be aware that Revolution is not good at killing any others at a routine dosing level. Please write back so we can discuss the “mite matter” further, Dr. Randolph

  5. I changed my cat from Frontline to Revolution three months ago. I took him to the veterinarian and he was admitted for dehydration and lethargy. No answers from blood work. He continued to get weaker and started having seizures. He died 9 days later. I had him tested for heartworms, FIV and all other common illnesses. He was an inside cat and 3 yrs old. I never thought about the change to Revolution till after he was gone. He also started developing tumors in lungs, brain and lymph areas. Do you think this could have been the problem?

    • Tammy, I believe you answered your question in the next to the last sentence. I don’t believe that the most aggressive carcinogens could cause cancer in 9 days, but the coincidence of having applied Revolution at the same time your kitty was decompensating ( ) from lymphoma appears to be the fact of the case. The only way to know for sure would have been to have taken specimens of the actual tumors, especially enlarged lymph nodes, but it’s much too late for that now. Lymphoma that didn’t affect the circulating lymphocytes would not have shown up on the blood tests. Feline Leukemia Virus ( ) can be sequestered in places in the body, and testing the blood won’t show sequestered virus. FeLV, then, can stimulate cancer, which fits the signs you’ve described. And, yes, even in a young, indoor, protected kitty. We are so very sorry for your loss, Dr. Randolph.

  6. Hi there–I gave my cat Revolution for the first time two days ago and she is acting strangely now. Before I gave her the medication she was having trouble with the extreme heat of the summer. She was hiding in cool corners, not engaging with me as usual and not very interested in her food. Now she has been more willing to engage with me; she is sleeping out in the open where I can see her, but she is lethargic, and not eating or drinking. It’s Saturday and she has an appointment with the veterinarian Monday, so I’m hoping she will start to perk up before then. If not, I will take her in to the emergency veterinarian. I have been feeding her water and electrolytes with an eye dropper, brushing her to get rid of extra fur she is shedding, and cooling her off with wet towels. She has vomited up some big hair balls (she usually doesn’t have any) and when I attempted to give her some wet food she took one sniff and immediately gagged. I think she is nauseous. Any encouraging words?…

    • I’m sorry I couldn’t get to your question Saturday. If you are a subscriber (it’s free!), you will note tomorrow’s post indicates our oldest granddaughter has been visiting us, so our time to do things other than with her has been limited. Some cats give a response like this to the placement of ANY medication (or even water) onto the body. Sometimes it’s a coincidence that your kitty was getting sick at the same time you happened to put on the Revolution. Some cats will develop an area of hair loss where the Revolution was administered. Rarely we see cats that act ill upon Revolution administration, and your pet’s doctor should report this to Pfizer as an “adverse event” if it turns out there are no illnesses to blame the condition on. I hope that you went to the emergency veterinarian’s office for care, as it sounds like the baby was quite ill. Either way, please write back so that I, and our readers, can know what the outcome was. Thanks for reading, and for writing, Dr. Randolph.

  7. Hello. We decided to let a stray cat come into our house. We have other cats so I gave the stray (otherwise perfectly healthy in appearance) a dose of Revolution to prevent the spread of fleas. The poor thing died a week later. Did I kill her by giving her the Revolution? I worry that maybe she had heartworms and it killed the worms and clogged her heart?

    • Lori, I certainly don’t want to put you on a guilt trip here, but it’s always important to have a pet examined by a veterinarian before using prescription medications. In addition, we all know not to use other people’s medications. Likewise, we shouldn’t use on pet’s medication on a pet the medcine was not prescribed for ( ). That said, Revolution is not very effective in killing adult heartworms and it is not a very good microfilaricide, either. The usual danger in giving heartworm preventive to pets with heartworms is that the heartworm preventive can kill microfilariae and result in a fatal reaction. Cats rarely have enough microfilariae to result in a reaction severe enough to be fatal. His death could have been caused by anything. NOW, your bigger concern is that the stray could have brought in Feline Leukemia Virus ( ), Feline Immunodeficiency Virus ( ) and/or intestinal parasites to infect your preexisting population of cats. You must call, make an appointment, have all of the cats “combo-tested” for both diseases, then have the tests repeated in two months (or at the interval your veterinarian recommends). Take a fresh stool sample from the litterbox (be sure to mark on the container which cat it came from) for each cat so they can be tested for intestinal parasites. Lastly, watch for an upcoming post about “Tracy” and “Subway,” which will tell the story of why we don’t allow un-examined pets to have contact with our healthy pets. Best wishes, Dr. Randolph.

  8. Dear Dr. Randolph, Does a cat have to be examined to have Revolution flea control prescribed? My cat was last examined December of 2008 (17 months ago). He is a healthy, happy cat who has been treated with Revolution monthly for 2+ years with no problems. His next shots are not due till next year and unless he is sick I do not want to take him in and really don’t have the money to spend if there is no reason. Is it required by law that he be examined (since it is more than a year since the last one) before his doctor can re-prescribe it?

    • Debbie, the decision about whether your pet HAS to be examined prior to Revolution dispensing has more to do with your pet’s doctor’s policies than law. I say that based on the fact that you already have a doctor-client-pet relationship with your veterinarian. No veterinarian is going to prescribe a prescription medication such as Revolution to a pet he has not seen. That WOULD be against the law. You and your kitty don’t fall into that category. Some food for thought:
      1, even though your veterinarian seems to use an extended vaccination schedule, he probably recommends (or even requires) annual examinations, the most important part of a pet’s visit. 2, Each veterinarian takes into account certain risk factors, which are different for each individual patient, in making the decision about what parameters must be met prior to dispensing medication. I am going to write a post for this Friday, which will give you more detail. Have you called to ask the doctor, or his staff, about a refill?

  9. I gave first dose ever of Revolution to my 11 yr. old Boston Terrier on June 1. On June 4 she had bloody diarrhea. There have been no dietary changes. She does not appear to be sick. Is the diarrhea from Revolution? If so, how long will it last? If so, should I skip the July dose?

    • I am likely the world’s biggest fan of Revolution. That said, I’m also the first to recognize that there are a few, rare problems with Revolution. However, if diarrhea is one of them, I’ve never seen it. It’s far more likely that this is mere coincidence. Most importantly, if diarrhea has continued since June 1 your Boston needs to see his doctor TODAY! If the diarrhea has stopped on its own and his appetite and activity remain normal there should be no more worry. In the unlikely case of recurrence of diarrhea after the July dose your local veterinarian must be contacted. I would like to have an update then, too. As I mentioned, I’ve never seen Revolution-associated diarrhea.
      Thanks for writing, Dr. Randolph.

    • Thank you for an excellent question. There are three parts to the answer:
      1. We’re not a pharmaceutical site, so we don’t sell anything.
      2. Revolution is a prescription medication, regulated by the Food and Drug Administration, just like every pharmaceutical at Rite Aid. In order for heartworm preventives to be dispensed the dispensing veterinarian has to have examined your pet and ensured that he is healthy enough to use a prescription medication. In the case of dogs, this also means he needs to have had a heartworm test within the last 6 months. If your pet has not been on heartworm preventive, or has missed doses, he would be at risk for having a bad, even possibly fatal reaction to the medication.
      3. I would suggest that you not purchase pharmaceuticals online, especially from people you don’t know. In my case, I’m the nicest, most ethical person you could ever meet, but not everyone online is. Your local veterinarian, however, is someone you know and trust. He may charge more for Revolution, but at least you know you’re getting REVOLUTION, and not a vial full of water, or worse. I hope this answers your concerns.
      Best wishes,
      Dr. Randolph

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.