Good To Know

Heart murmurs in cats are often detected during a routine physical exam by listening to the heart with a stethoscope. A disturbance in the blood flow produces a “whooshing” sound or another noise in addition to the heartbeat.

What causes a heart murmur?

A heart murmur is caused by turbulent blood flow within the heart. Some murmurs are considered innocent or phsyiologic. These murmurs, while not considered normal, have no impact on the cat’s health. Common causes of heart murmurs are hyperthyroidism, high blood pressure, a thickening of the heart muscle, or heart disease.

Not all heart murmurs are created equal

Not all heart murmurs sound the same. The loudness of a murmur doesn’t necessarily correlate to the severity of disease. Murmurs are graded by intensity on a scale of I through VI.

  • Grade I—barely audible
  • Grade II—soft, but easily heard with a stethoscope
  • Grade III—intermediate loudness; most murmurs which are related to the mechanics of blood circulation are at least grade III
  • Grade IV—loud murmur that radiates widely, often including opposite side of chest
  • Grade V—very loud, audible with stethoscope barely touching the chest; the vibration is also strong enough to be felt through the animal’s chest wall
  • Grade VI—very loud, audible with stethoscope barely touching the chest; the vibration is also strong enough to be felt through the animal’s chest wall

Grading scale via PetMd

Murmurs are also characterized by location, by which time in the heart cycle they occur, where they are the loudest, and whether they’re long or short. The specific details of a heart murmur will help your veterinarian identify what is causing the murmur and whether further diagnostics are needed.

Heart murmurs can be difficult to detect

It takes a skilled veterinarian to detect some heart murmurs. The severity of murmurs can vary from one exam to the next. Some cats will have murmurs as a result of stress. A mild murmur  may be worse if a cat is dehydrated. If a cat is breathing hard, or if the cat’s human or a veterinary assistant are petting the cat during the exam, inexperienced vets may interpret the resulting sounds as a murmur. Murmurs may also be missed due to a poor quality stethoscope. Ideally, your vet should listen to your cat’s heart for a minute or two rather than just for a few seconds.


If a murmur is detected in a very young kitten, your vet may recommend a recheck exam after the kitten is four months old. While heart murmurs in very young kittens can be an indicator of a congenital defect, they can also be innocent murmurs that will disappear without intervention.

For an adult cat, further testing will be recommended, including radiographs, an electrocardiogram, and an echocardiogram (ultrasound of the heart.) If you vet suspects that the murmur is caused by another underlying disease, blood tests will also be required.

The most reliable test to diagnose heart disease is an echocardiogram with a Doppler examination. This specialized type of echocardiogram will measure the speed and direction of blood flow across the heart valves and in the heart chambers.

Some general practitioners will be able to perform ultrasound examinations in their clinics; however, reading a cardiac ultrasound properly requires advanced training. Anytime your cat is diagnosed with a heart murmur or other condition that affects the  heart, a consultation with a veterinary cardiologist is recommended.

Treatment and prognosis

Treatment and prognosis will depend on the cause of the murmur and any underling disease processes, and may include a combination of medication, supportive care and continued monitoring. Prognosis will vary depending on the severity of the disease.

This post was first published in 2015 and has been updated.

Image Depositphotos

13 Comments on Heart Murmurs in Cats

  1. My vet thinks my kitten has a heart murmur but can’t fully tell. He’s only 6 weeks old and she didn’t listen for that long. She said it was incredibly uncommon in cats but especially kittens. It’s making me incredible nervous until his next vet appointment…but I also feel like she didn’t take into account how anxious he was from being there and he hates the carrier!

  2. My cat Hankie had a grade 4 murmur. He died in February from a saddle thrombus, (blood clot) probably caused by the heart problem. He was 7 years old. I think I read on this site about the thrombus and then did some research and was glad I did. It’s an extremely painful problem and usually fatal. I went to emergency vet as soon as I saw the symptoms and had to put him down. My consolation was he didn’t suffer too much. Miss him very much

  3. My kitty, Eloise, on meds for lymphoma also has a heart murmur. Vet called with latest blood work result… said he had a certain test done to measure something about her heart (I was at work and couldn’t concentrate well)… said test scale is 10 to 100 and she came in at 102. Very high for muscle damage? Taking her back next month for monthly check up. I don’t want to stress her with any more meds. Have to watch her for signs of respiratory distress (so far, none)… she just has a poor appetite. If only our furbabies could talk and tell us what they’re feeling. 🙁

  4. I was totally captivated by this article, Ingrid. My own human heart murmur has been with me all my life and they think it’s genetic. However, now that I’m older it’s affecting my heart to the extent of actually being diagnosed with congenital heart disease. Amazing how this can translate into our kitties. Mine just went for their shots and exams and no problems were detected except for the trauma of being in the carrier and the car, not to mention my trauma listening to them setting each other off. No ill effects once we were home again, however.

    • Sorry to hear that. On the plus side, my dad has had a heart murmur, and he’s 95 now. We think his jogging and walking since the 1970’s helped. I have a kitty now that has a heart murmur, will ask his vet what “grade.” Thanks for the info!

  5. Very interesting. I thought they only went to grade 4. I have several cats with murmurs, but none require meds at this time.

  6. My cat Squeaky had a heart murmur but; it must of not been a bad one cause they told me not to worry. Just have check ups.

  7. My Socky had a heart murmur from her first visit to the last. She would often be passed around the hospital for all to hear. They insisted I put her on medicine and get further testing done.
    She was a wild stray I raised from the day her eyes opened. Her mother was accidently killed while in a wood pile. I was poor and really couldn’t afford treatment.
    She lived to the ripe old age of 20 human years weighing in at 5 pounds. She was always a tiny thing but lived a long happy life medicine free.
    This may not be the path for everyone, but it worked well for our beloved kitty who now has wings.

    • That’s amazing that Socky lived to be 20, even though she had a heart murmur all her life. Just goes to show that some murmurs don’t require treatment.

  8. My cat, Bunny, had a grade 4 murmur. She lived to 17.5 years. Apparently she had the innocent type of murmur as she had no comorbidities and required no meds. She’s been gone 11 years now, and still, every April 19, I recite the story of how we found each other on that Sunday in 1987.

  9. Thank you for the informative article, Ingrid. Our vet thought she heard a murmur in Lita once, but she has since said she doesn’t hear it anymore, so it may have been caused by stress like you mentioned.

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