Your Vet Heard a Heart Murmur. Here’s What Happens Next.

It usually happens during a routine visit. Your vet listens to your pet’s chest, pauses, moves the stethoscope, and listens again. Then you hear it: “I’m picking up a heart murmur.”

For a lot of pet parents, everything after that sentence is a blur.

So here’s the first thing to know. A murmur is a sound, not a diagnosis. It tells your veterinarian that blood is moving through the heart in a way that deserves a closer look. What’s causing it, and whether it needs treatment at all, is what the next steps are for.

What is a heart murmur in dogs and cats?

A healthy heartbeat makes two sounds, the familiar lub and dub, as the heart’s valves close. A murmur is an extra sound mixed in, often described as a whoosh. It happens when blood flow inside the heart, or in the large blood vessels right next to it, turns turbulent instead of smooth.

Plenty of things can cause that turbulence. A valve that no longer closes tightly. A narrowed opening a pet was born with. Heart muscle that has thickened. Sometimes there’s no heart problem at all: anemia, fever, or a fast heart rate can make normal blood flow loud enough to hear. In cats, an overactive thyroid is another cause vets check for.

That’s why a murmur on its own doesn’t tell your vet what’s wrong. It tells them where to start looking.

What does a heart murmur grade mean?

Veterinarians grade murmurs by loudness on a scale of 1 to 6. You may see it written as a fraction, like 3/6, which simply means grade 3 out of 6.

Your vet may also note where on the chest the murmur is loudest and when it happens in the heartbeat. Those details help narrow down the cause, so write them down along with the grade.

Does a louder murmur mean more serious heart disease?

Sometimes. Not reliably enough to use loudness as the answer.

In small breed dogs with the most common adult heart condition, a valve disease called myxomatous mitral valve disease (MMVD), loudness and severity do tend to move together. A large study of these dogs found that most dogs with the softest murmurs did not have enlarged hearts, while the loudest murmurs, the ones strong enough to feel through the chest, were linked with more advanced disease. The dogs in between were a mixed group. Some had enlarged hearts and some didn’t, so a middle grade murmur said much less about any one dog.

Other conditions don’t follow that pattern. Dogs with dilated cardiomyopathy (DCM), a disease of the heart muscle seen more often in larger breeds, can have a soft murmur or no murmur at all.

Heart murmurs in cats

Murmurs are common in cats, including cats whose hearts turn out to be normal on imaging. At the same time, many cats with hypertrophic cardiomyopathy (HCM), the most common form of heart disease in cats, have no murmur at all. Even a murmur that gets louder over time doesn’t necessarily mean heart disease is present or getting worse.

Because the sound is such an unreliable guide in cats, veterinary cardiology guidelines recommend following up on a murmur found in any cat, including one who seems perfectly healthy.

The tests that usually come next

The murmur is the clue. Testing is how your vet finds out what’s behind it. Here’s what may be recommended and what each test shows.

Chest x-rays

Chest x-rays show the size and shape of the heart and whether fluid is building up in or around the lungs. Just as important, they give you a baseline. When your vet repeats the x-rays later, they can put the images side by side and see whether the heart’s size has changed.

In dogs, vets often measure heart size on an x-ray using something called a vertebral heart score. Ask for the number and keep it with your pet’s records.

Echocardiogram

An echocardiogram is an ultrasound of the heart. If you’ve ever seen an ultrasound during a pregnancy, it’s the same basic idea. A probe rests against the chest and shows the heart moving in real time: the valves, the thickness of the heart muscle, the size of each chamber, and the direction the blood is flowing.

This is the test veterinarians rely on most to answer the question the murmur raised. Was your pet born with a defect? Is a valve leaking? Is the heart muscle thickened or weakened? Or is the heart normal, with a harmless flow murmur? The echocardiogram is also how many heart conditions are staged, and the stage shapes what your vet recommends next.

Many pets lie on a padded table for the scan without sedation, though some are given a mild sedative to help them stay still.

Blood tests

Your vet may also suggest a blood test called NT-proBNP. It measures a substance the heart releases when its muscle is stretched or under strain. It can’t identify a specific condition, but it can help your vet decide whether imaging should be the next step. It’s used often in cats.

Should you see a veterinary cardiologist?

Your regular vet can take x-rays and run blood work. For an echocardiogram, many will refer you to a veterinary cardiologist.

A lot of pet parents don’t know these specialists exist. A board-certified veterinary cardiologist is a veterinarian who completed years of additional training focused on the heart and passed specialty exams through the American College of Veterinary Internal Medicine (ACVIM). Hearts are what they look at all day.

A referral can feel alarming, as if your vet suspects something terrible. Often it just means your vet wants the clearest answer available. You can search for a board-certified cardiologist near you in ACVIM’s directory at VetSpecialists.com.

Before the appointment, write your questions down. A few worth bringing:

• What is causing the murmur?
• Is my pet’s heart enlarged?
• What stage is this, and what does that stage mean?
• Does my pet need medication now, or do we watch and recheck?
• When should we repeat the x-rays or the echocardiogram?
• Should I be counting my pet’s breathing rate while they sleep?
• What changes at home mean I should call you right away?

If your vet prescribes heart medication

Depending on what testing shows, your veterinarian may recommend monitoring only, or they may prescribe medication. Pimobendan, enalapril, and spironolactone are a few of the names pet parents commonly hear. They work in different ways and may be prescribed alone or together. Which medications fit your pet, if any, is a decision for your veterinarian or cardiologist. If pimobendan is on the list, our guide to how pimobendan works explains it in plain language.

Once there’s a prescription, the questions usually turn practical. Should it be given with food? What time of day? What happens if I miss a dose? Those are questions for our pharmacy team, and you can call us about any medication we dispense. If your pet refuses the pill, we have a separate guide on how our pharmacy can help when a pet won’t take medication.

Can your dog’s food affect heart health?

Diet comes up in heart conversations too, especially with dogs.

Since 2018, regulators and veterinary researchers have been looking into reports of dilated cardiomyopathy in dogs eating certain diets, many labeled grain free, with peas, lentils, other legumes, or potatoes among the main ingredients. Some of those dogs were breeds not usually prone to DCM. The research is ongoing, and a cause has not been proven. And as mentioned above, DCM doesn’t always come with a loud murmur, which is one more reason testing matters.

Tell your veterinarian exactly what your dog eats: the brand, the specific formula, treats, and anything you add to the bowl. A photo of the ingredient list works fine. And talk to your vet before switching foods, so any change is part of the plan rather than a guess.

When to call your vet right away

Many murmurs turn up at routine visits in pets who seem completely fine. Still, some signs shouldn’t wait for the next appointment:

• Fast or labored breathing while your pet is resting or asleep
• Coughing in dogs, especially at night
• Tiring much faster than usual on walks or during play
• Fainting or collapsing
• Gums that look pale, gray, or bluish
• A swollen belly
• In cats, sudden weakness, pain, or dragging of the back legs

If your pet is struggling to breathe or collapses, go straight to an emergency veterinarian.

Frequently asked questions

Can a dog live a normal life with a heart murmur?

It depends entirely on the cause. Some murmurs are harmless, and some heart conditions stay mild for years. Others progress. Testing is what tells you which situation your dog is in, and your veterinarian can explain what to expect for your dog specifically.

What is a grade 3 heart murmur in a dog?

It’s a murmur of moderate loudness on the 1 to 6 scale, clearly heard as soon as the vet starts listening. On its own, a grade 3 murmur doesn’t tell you how advanced a heart condition is. Imaging answers that.

Is a heart murmur in a puppy serious?

Puppies sometimes have a soft murmur that isn’t caused by any heart problem, often called an innocent murmur. Many of these fade as the puppy grows, commonly by around 4 to 6 months of age. A murmur that is loud or doesn’t go away needs a closer look, because some puppies are born with heart defects. Expect your vet to recheck it at future visits.

Can a heart murmur go away?

Innocent murmurs in puppies often do. A murmur caused by fever or anemia can fade once that problem is addressed. Murmurs caused by structural heart disease generally don’t go away on their own.

Do cats with heart disease always have a murmur?

No. Many cats with hypertrophic cardiomyopathy have no murmur, and many cats with a murmur have normal hearts. That’s why veterinary guidelines recommend following up on a murmur found in any cat.

A murmur is where the questions start

Hearing the word murmur is scary. What it really gives you is a starting point. Get the baseline x-rays. Ask whether an echocardiogram makes sense for your pet, and whether a cardiologist should perform it. Bring your questions written down. Each answer makes the next decision a little clearer.