What Does a Heart Murmur Actually Mean for Your Cat?

Your vet just mentioned a heart murmur at your cat’s checkup, and now you’re home trying to figure out if this is serious. First: take a breath. A heart murmur isn’t a diagnosis. It’s a sound, an abnormal whoosh or swish the vet hears through a stethoscope when blood flows through the heart irregularly. Some murmurs turn out to be nothing. Others point to an underlying condition that needs attention. The grade your vet assigned tells you how loud it is, not how serious it is. Here’s what you need to know.

What heart murmur grades actually mean

Vets grade heart murmurs in cats on a scale of 1 to 6. That number tells you how loud the sound is when heard through a stethoscope. It does not tell you how damaged the heart is, or how sick your cat will get. A loud murmur can come from a benign cause, and a quiet one can come from serious disease.

• Grade 1: Very faint, often only heard in a quiet room by an experienced vet. Usually an incidental finding that surprises both vet and owner.
• Grade 2: Soft but consistently audible. Often picked up at routine exams.
• Grade 3: Moderate loudness. This is typically the point where your vet will start recommending a closer look.
• Grade 4: Loud and clearly present. Audible across different areas of the chest.
• Grade 5: Very loud. Your vet can actually feel a faint vibration on the chest wall, which is called a thrill.
• Grade 6: The loudest possible. That vibration is felt even when the stethoscope is barely touching the chest.

A grade 3 heart murmur in cats or above is generally the threshold where vets start recommending an echocardiogram. But even a grade 1 or grade 2 heart murmur in cats warrants monitoring and follow-up, especially in breeds predisposed to heart disease.

What causes a heart murmur in cats?

The murmur itself isn’t the problem. It’s a symptom of something else happening in the body. The most important thing is figuring out what’s behind it.

Hypertrophic cardiomyopathy (HCM)

HCM in cats is by far the most common cause of a feline heart murmur. It’s a condition where the heart muscle becomes abnormally thick, making it harder for the heart to fill and pump blood properly. Maine Coons, Ragdolls, Persians, and Sphynx cats have a known genetic predisposition, but any cat can develop it, including young cats and seniors.

Other structural heart conditions

Congenital heart murmurs in cats, meaning those present from birth, can be caused by structural defects like patent ductus arteriosus (PDA), a blood vessel near the heart that fails to close properly after birth. These are more common in young cats and kittens, and some may require surgical correction.

Physiologic or innocent murmurs

Sometimes a murmur has no structural cause at all. Anemia (low red blood cell count, which makes blood thinner and faster-moving), hyperthyroidism (an overactive thyroid gland, common in senior cats), fever, and even stress can all create a murmur-like sound that disappears once the underlying issue is resolved. These are sometimes called innocent heart murmurs. Stress-induced murmurs are especially common at the vet’s office, where an anxious cat’s heart rate spikes. If your vet suspects this, they may ask you to come back for a recheck when your cat is calmer.

Symptoms to watch for at home

Many cats with heart murmurs, especially low-grade ones, show zero symptoms for months or years. The murmur gets found at a routine exam while everything else looks fine. But as heart disease progresses, you may start to notice:

• Faster or labored breathing, especially at rest
• Open-mouth breathing (always a red flag in cats)
• Reduced energy or reluctance to play
• Hiding more than usual
• Weight loss or decreased appetite
• Weakness in the back legs (can signal a blood clot, which is a cardiac emergency)

If your cat suddenly can’t use their back legs, is crying out in pain, or is breathing with their mouth open, go to an emergency vet immediately. Don’t wait to see if it passes.

What happens after a heart murmur is found?

Hearing a murmur through a stethoscope is just the starting point. To understand what’s actually going on inside the heart, your vet will likely recommend one or more of the following:

• Echocardiogram: A heart ultrasound that lets a veterinary cardiologist see the heart’s structure and function in real time. This is the gold standard for diagnosing HCM and other cardiac conditions in cats.
• NT-proBNP test: A blood test that measures a protein released when the heart is under stress. Elevated levels suggest cardiac disease is present, even before obvious symptoms appear.
• Chest X-rays: Shows whether the heart looks enlarged or whether fluid has started building up in the lungs, both of which can signal congestive heart failure.
• Bloodwork and thyroid testing: Helps rule out non-cardiac causes like anemia or hyperthyroidism.
• ECG (electrocardiogram): Checks for arrhythmia, meaning irregular heart rhythms that can accompany structural heart disease.

Once the diagnostic picture is clear, your vet or veterinary cardiologist will put together a treatment plan based on what’s actually driving the murmur. There’s no treatment that fixes a murmur directly. What vets treat is the underlying cause.

For cats with HCM, medications like beta-blockers or calcium channel blockers may be prescribed to help the heart work more efficiently. If congestive heart failure develops, diuretics help remove excess fluid from the lungs and are often a core part of keeping your cat comfortable.

Life expectancy varies widely depending on the underlying condition and how advanced it is at diagnosis. A cat with a low-grade murmur from a non-cardiac cause may live a completely normal life. A cat with HCM that hasn’t progressed to heart failure can remain stable for years with the right monitoring. Once congestive heart failure develops, median survival is typically in the range of 6 to 18 months, though some cats do better with consistent management. The most honest picture of what to expect for your specific cat will come from your veterinary cardiologist, who knows your cat’s case.

How to monitor your cat’s resting respiratory rate at home

Congestive heart failure in cats often shows up first as a subtle increase in breathing rate, even while your cat is asleep. Monitoring your cat’s resting respiratory rate (RRR) is one of the simplest and most useful things you can do between vet visits.

Wait until your cat is deeply asleep, then count chest rises for 30 seconds and multiply by two. That’s your number. Under 30 breaths per minute is normal. At or above 30, call your vet even if your cat seems fine otherwise. A sudden jump of 10 or more breaths above your cat’s usual baseline is also worth a same-day call.

Log the number, date, and time each day. A simple notes app works fine. Bring that log to every appointment. A trend over time tells your vet far more than a single in-clinic reading, especially since cats often breathe faster at the vet due to stress.

Does pet insurance cover heart murmurs in cats?

Cardiac workups aren’t cheap. An echocardiogram with a veterinary cardiologist can run several hundred dollars, and ongoing medication or specialist follow-ups add up fast. That’s where having coverage while your pet is healthy matters.

A Lemonade accident and illness policy can help cover eligible costs related to heart conditions like HCM, including echocardiograms, diagnostic testing like NT-proBNP, and treatment for congestive heart failure, as long as the condition isn’t pre-existing and your waiting periods have passed. If a murmur is already noted in your cat’s medical records, related cardiac conditions may be excluded from a new policy. The earlier you enroll, the more coverage can actually do for you when you need it.

Before we go

A heart murmur is scary to hear about, but it’s not a verdict. It’s a signal that your cat’s heart deserves a closer look. Ask your vet about an echocardiogram referral, start logging your cat’s resting respiratory rate tonight, and bring that log to every appointment. The more information your vet team has, the better equipped they’ll be to catch any changes early. And if your cat isn’t already covered, now is a good time to look into it. Get a quote with Lemonade in minutes.

Frequently Asked Questions

A few quick words, because we <3 our lawyers: This post is general in nature, and any statement in it doesn’t alter the terms, conditions, exclusions, or limitations of the policies issued, which differ according to your state of residence. You’re encouraged to discuss your specific circumstances with your own professional advisors. The purpose of this post is merely to provide you with info and insights you can use to make such discussions more productive! Naturally, all comments by, or references to, third parties represent their own views, and Lemonade assumes no responsibility for them. Coverage may not be available in all states. Please note that statements about coverages, policy management, claims processes, Giveback, and customer support apply to policies underwritten by Lemonade Insurance Company or Metromile Insurance Company, a Lemonade company, sold by Lemonade Insurance Agency, LLC.  The statements do not apply to policies underwritten by other carriers.