Cats With Heart Murmurs Facts & Insights

Hearing that your cat has a heart murmur can feel scary, especially when it comes out of nowhere at a routine exam. Take a breath. A murmur is a finding, not a diagnosis, and many cats with murmurs live normal, happy lives. The key is understanding what a murmur means, what it can (and cannot) tell us, and what the next best steps are.

As a veterinary assistant, I have seen this go two ways: sometimes the murmur is truly “innocent” and never causes a problem. Other times, it is the first clue that we need to look closer at the heart. This article walks you through current, evidence-informed guidance so you can advocate for your cat with confidence.

What a heart murmur is

A heart murmur is an extra sound heard during a heartbeat cycle. Instead of the normal “lub-dub,” the veterinarian hears a whooshing sound created by turbulent blood flow. That turbulence can happen for many reasons, and not all of them are dangerous.

Murmur versus heart disease

This is one of the most important distinctions:

• A murmur is something your veterinarian hears with a stethoscope.
• Heart disease is a structural or functional problem of the heart.
• Heart failure is when the heart can no longer keep up with the body’s needs, leading to issues like fluid in or around the lungs.

A cat can have a murmur and never develop heart failure. And a cat can have significant heart disease with no murmur at all. That is why follow-up testing matters.

Common causes in cats

In cats, murmurs can come from:

• Primary heart disease such as hypertrophic cardiomyopathy (HCM), one of the most commonly diagnosed heart diseases in cats.
• Physiologic or “innocent” murmurs where the heart is structurally normal, but blood flow is temporarily faster or more turbulent (this can happen in kittens and young cats, too).
• Secondary causes like anemia, fever, dehydration, high blood pressure, or hyperthyroidism in older cats.
• Stress and excitement which can raise heart rate and make mild murmurs easier to hear during an exam.

Because cats can be masters at hiding illness, your veterinarian will often recommend basic screening if there is any suspicion of an underlying cause, especially in senior cats.

One practical note: because stress and handling can change what we hear, your veterinarian may recommend a recheck in a calmer setting, or after addressing pain or anxiety, if the rest of the exam is reassuring.

How murmurs are graded

Murmurs are often graded on a scale of I to VI:

• Grade I: very soft, hard to hear
• Grade II: soft but clear
• Grade III: moderate
• Grade IV: loud
• Grade V: very loud, may be felt as a vibration (thrill)
• Grade VI: extremely loud, audible with the stethoscope barely touching

Here is the insight many cat parents miss: louder does not always mean more severe disease in cats, and a soft murmur does not guarantee everything is fine. Murmur grade is just one piece of the puzzle.

Also, not all murmurs are the same type. Most are systolic, but diastolic or continuous murmurs are uncommon and may be more concerning, which is one reason your vet might recommend a workup even if your cat seems fine.

Signs at home

Many cats with a murmur look completely normal at home. When symptoms do happen, they may be subtle until the situation is urgent.

Watch for these signs

• Decreased activity or tiring faster during play
• Hiding more than usual
• Reduced appetite or weight loss
• Rapid breathing while resting or sleeping
• Open-mouth breathing (this is an emergency in cats)
• Fainting or collapse (urgent)
• Sudden hind limb weakness or pain (could be a clot, urgent emergency)

If you are ever unsure about breathing, count it. A helpful home habit is checking your cat’s resting respiratory rate when they are truly asleep or fully relaxed.

• Many healthy cats rest around 16 to 30 breaths per minute.
• If your cat is consistently over 30 to 35, call your veterinarian for advice.
• Over 40, or any obvious effort to breathe, should be treated as urgent.

Tip: one breath is a chest rise and fall.

Most useful tests

Because a murmur is a sound, the next step is to evaluate the heart itself and look for underlying conditions that can create turbulent flow.

Echocardiogram (cardiac ultrasound)

An echocardiogram is the most definitive test for evaluating heart structure and function. It can identify conditions like HCM (a common feline issue), assess heart chamber size, and evaluate how well the heart is pumping. It can also assess valves, although primary valve disease is less common in cats than in dogs. This is typically performed by a veterinary cardiologist or a veterinarian with advanced ultrasound training.

Bloodwork

Basic bloodwork (often a CBC and chemistry) helps check for anemia and provides a snapshot of overall health and organ function, which matters when choosing medications and monitoring safety.

Thyroid testing (especially in older cats)

Hyperthyroidism can increase heart rate and workload, sometimes creating or worsening murmurs and heart changes. Treating thyroid disease can significantly reduce cardiac stress in many cats.

Blood pressure

High blood pressure is common in senior cats and can affect the heart, kidneys, eyes, and brain. If your cat has a murmur and is older, a blood pressure reading is often a smart move.

Chest x-rays

X-rays do not diagnose HCM by themselves, but they can show heart enlargement or fluid in or around the lungs, which is critical when breathing signs are present. Keep in mind that radiographs can look normal in some cats with cardiomyopathy, so normal x-rays do not rule out heart disease.

NT-proBNP (heart biomarker)

Your veterinarian may recommend an NT-proBNP test (a blood test) to help assess whether heart disease is more likely. It can be useful as a screening tool, but it does not replace an echocardiogram.

Treatment basics

Treatment depends on the cause of the murmur, not the murmur itself.

If the heart is normal

If an echocardiogram shows no structural heart disease and secondary causes are ruled out, your veterinarian may simply recommend periodic rechecks. Some cats have transient murmurs that come and go.

If your cat has heart disease but no heart failure

Some cats with early HCM may not need medication right away. Others may benefit from tailored therapy based on heart function, rhythm, and risk factors. Your vet or cardiologist will guide this.

If your cat has congestive heart failure

This is when medication becomes essential. Common approaches may include diuretics to reduce fluid and other medications chosen based on the specific heart findings. Always give meds exactly as directed and do not stop suddenly unless your veterinarian tells you to.

Home care tips

You do not have to become a cardiologist to care well for a cat with a murmur. The goal is to support overall health, catch changes early, and reduce stress.

• Track resting breathing a few times per week and write it down.
• Keep play gentle and cat-led. Let your cat choose the pace.
• Maintain a lean body condition. Extra weight increases workload on the heart and the whole body.
• Schedule regular veterinary checkups, especially for senior cats.
• Ask before adding supplements. “Natural” does not always mean safe, especially with cardiac medications.
• Reduce stress with predictable routines, quiet resting areas, and gradual changes in the home.

Breeds and genetics

Some purebred lines have higher risk for inherited heart disease, including HCM. Maine Coons and Ragdolls are commonly discussed in the research and breeding communities, but HCM can occur in any cat, including mixed breeds.

If you have a kitten or young adult cat with a murmur, your veterinarian may recommend a cardiology consult sooner rather than later, especially if there is a family history of heart disease or sudden death.

When it is an emergency

A murmur alone is rarely an emergency. The emergency is the symptoms that can accompany advanced heart disease.

Seek emergency care right away if you see:

• Open-mouth breathing or severe labored breathing
• Blue or gray gums
• Collapse or sudden extreme weakness
• Sudden hind limb paralysis or intense pain (possible arterial clot)

If you are driving to an emergency clinic, keep your cat warm, quiet, and in a carrier. Do not force food, water, or medications unless a veterinarian instructs you to.

Questions to ask your vet

Going into your next visit with a short list can make the appointment less overwhelming:

• What murmur grade did you hear, and where was it loudest?
• Did you notice an abnormal rhythm (arrhythmia) or gallop sound?
• Do you recommend an echocardiogram now, or monitoring first?
• Should we check blood pressure and thyroid levels?
• What home signs should prompt a same-day call?
• How often should we recheck, and what will we listen for?

Most cats do best when we focus on early detection, appropriate testing, and calm, consistent follow-up. A murmur is information, and information is power.