A heart murmur in dogs is an extra whooshing sound your veterinarian hears through a stethoscope, caused by turbulent blood flow in or around the heart. A murmur is a sign, not a diagnosis on its own, so your veterinarian grades it from 1 to 6 and uses further tests to find the cause. Many dogs with a soft murmur live comfortable, active lives, while others need ongoing monitoring and, in some cases, prescription medicine decided by the vet.
If your dog was just diagnosed with a heart murmur, take a breath. This guide explains what the grades mean, what causes murmurs, the symptoms to watch for, and how everyday care fits into the plan your veterinarian sets.
A cat resting comfortably at home.
What is a heart murmur in a dog?
A heart murmur in a dog is an abnormal sound created when blood moves through the heart with more turbulence than usual. Instead of the normal clean "lub-dub", your veterinarian hears an added swishing or whooshing noise during the heartbeat.
The murmur itself is not a disease. It is a clue that points your veterinarian toward further questions: Where is the turbulence coming from? How loud is it? And is the heart still working well?
Murmurs happen in both cats and dogs, but this article focuses on dogs. In dogs, murmurs are often linked to the heart valves, especially in smaller and older breeds.
Some murmurs are harmless, especially soft ones in young puppies that fade with age. Others reflect a structural change in the heart that needs attention. Only your veterinarian can tell these apart, so a murmur always deserves a proper check.
What do heart murmur grades in dogs mean?
Heart murmur grades in dogs run from 1 to 6, describing how loud the murmur is, not how sick the dog is. A grade 1 murmur is very faint and hard to hear, while a grade 6 murmur is so loud it can be felt through the chest wall with a hand.
Grading helps your veterinarian track changes over time and decide what further testing makes sense. A louder murmur does not always mean a sicker dog, but a murmur that climbs in grade over months is a reason to look more closely.
The grading scale at a glance
| Grade | How loud it is | What it may suggest |
| 1 | Very soft, heard only after careful listening | Often mild, needs monitoring |
| 2 | Soft but heard fairly easily | Usually mild, vet will track it |
| 3 | Moderate, clearly audible | Warrants further heart tests |
| 4 | Loud, no thrill felt on the chest | Often reflects a real heart change |
| 5 | Loud with a palpable thrill on the chest | Significant, needs full workup |
| 6 | Very loud, felt with the stethoscope barely touching | Significant, needs full workup |
A "thrill" is a vibration an examiner can feel with a flat hand on the chest. Grades 5 and 6 include this vibration.
Remember that grade describes volume, not function. A dog with a grade 2 murmur may still need careful follow-up, and a dog with a grade 4 murmur may feel well for a long time. Your veterinarian interprets the grade alongside everything else they find.
What causes a heart murmur in dogs?
Heart murmurs in dogs are most often caused by changes in the heart valves that let blood leak backward, but they can also come from thickened heart muscle, congenital defects present from birth, or non-heart causes such as anemia. The exact cause shapes the whole care plan, which is why your veterinarian investigates beyond the sound itself.
Common reasons behind a canine murmur include:
- Degenerative valve disease, where a heart valve thickens and no longer seals tightly. This is especially common in small and middle-aged to older dogs.
- Dilated heart muscle, where the heart chamber stretches and pumps less efficiently. This is seen more often in larger breeds.
- Congenital heart defects, structural differences a puppy is born with.
- Non-heart causes, such as anemia or fever, which can create a murmur even when the heart structure is normal.
Breed, age and size all play a role, so your veterinarian weighs these factors together. Supporting a dog through a long-term heart condition is similar in spirit to how owners support a dog's recovery from chronic disease with the right daily care, always guided by the vet.
Because the same murmur sound can have very different causes, pinning down the reason is a job for your veterinarian and their diagnostic tools.
What are the symptoms of a heart murmur in dogs?
Many dogs with a heart murmur show no symptoms at all, which is why murmurs are often found during a routine check-up. When symptoms do appear, the most common early signs are coughing, tiring quickly on walks, and faster or harder breathing at rest.
Signs to watch for in dogs include:
- A cough, especially at night or after lying down
- Getting tired or short of breath sooner than usual on walks
- Faster breathing or more effort to breathe while resting
- Reduced appetite or gradual weight loss
- Restlessness or trouble settling at night
- Fainting or sudden weakness in more advanced cases
A useful home habit is counting your dog's breaths while they sleep. Your veterinarian can tell you what resting breathing rate is normal for your dog and when a rising number should prompt a call.
These signs can overlap with other conditions, so they are a reason to book a visit rather than to self-diagnose. If your dog ever struggles to breathe, has blue-tinged gums, or collapses, treat it as an emergency and contact a veterinarian right away.
How do vets diagnose and monitor dog heart disease?
Veterinarians diagnose and monitor dog heart disease by combining a physical exam with imaging and other tests, because the murmur grade alone cannot reveal how the heart is working. The most informative test is usually an echocardiogram, an ultrasound of the heart, often paired with chest X-rays and sometimes an ECG and blood tests.
Here is how the process often unfolds:
- Listening and grading. Your veterinarian hears the murmur, grades it, and notes the heart rhythm.
- Chest X-rays. These show the heart's size and whether fluid is building up in or around the lungs.
- Echocardiogram. This ultrasound shows the valves, chambers and pumping action in real time.
- ECG. This records the electrical rhythm if an irregular heartbeat is suspected.
- Blood and urine tests. These check overall health and organ function, which matters when planning long-term care.
Monitoring is ongoing rather than one-time. Your veterinarian may recheck the murmur, repeat imaging, and ask you to track resting breathing rate and energy at home.
What the vet checks at each stage
| Stage | What the vet looks at | Why it matters |
| First finding | Murmur grade, heart rhythm | Sets a baseline to compare against |
| Workup | Echo, X-rays, ECG, bloodwork | Identifies the cause and severity |
| Ongoing care | Breathing rate, weight, energy, repeat imaging | Catches changes early |
Dog heart disease monitoring is a partnership. Your notes from home and the vet's tests together give the clearest picture, so keep a simple log and share it at each visit.
Is a heart murmur the same as congestive heart failure?
No. A heart murmur is a sound, while congestive heart failure is a later stage where the heart can no longer keep fluid from backing up into or around the lungs. Many dogs live with a murmur for a long time and never progress to heart failure, so a murmur is a reason to monitor, not a reason to panic.
Congestive heart failure risk in dogs depends on the underlying cause, the severity of the heart change, and how early problems are caught. Signs that the situation is becoming more serious include increased resting breathing rate, a persistent cough, and reduced stamina.
This is exactly why regular monitoring matters. Catching changes early gives your veterinarian more options to keep your dog comfortable. Your veterinarian is the one who decides whether and when extra support or medicine is needed.
How is a dog heart murmur managed long term?
Long-term management of a dog heart murmur is built around regular veterinary monitoring, a suitable diet, a comfortable activity level, and, when the vet decides it is needed, prescription heart medicine. There is no single plan for every dog, because the right approach depends on the cause and stage of the heart condition.
Practical everyday steps many owners can take include:
- Keep every recheck appointment so your veterinarian can catch changes early.
- Track resting breathing rate and jot down coughing, energy and appetite.
- Follow your vet's diet guidance, which often means watching sodium and keeping a healthy weight.
- Keep exercise gentle and steady rather than intense bursts, as advised by your vet.
- Give any medicines exactly as prescribed, never adjusting the plan on your own.
Weight control and good general health matter, and some owners explore daily nutritional support for other organs under veterinary guidance, such as LiverRx for liver health or KidneyRx for kidney support when a dog has more than one condition. Always let your veterinarian coordinate the full picture.
Where does prescription heart medicine fit in?
HeartRx is a prescription heart medicine (pimobendan) your veterinarian may prescribe when they decide it suits your dog's specific heart condition. Because it is prescription only, the decision to use it, and how it is given, always rests with your veterinarian after proper testing.
Pimobendan is used in dogs as part of a vet-directed plan, not as something to buy or start on your own. If you want to understand how it works within a care plan, you can read more in this overview of HeartRx for dog owners and a broader look at why HeartRx is designed for cats and dogs.
Never change a dose, skip days, or stop heart medicine without speaking to your veterinarian first. The dosing details belong on the pack label and in your vet's directions, tailored to your individual dog.
FAQ
Can a dog live a long life with a heart murmur?
Yes, many dogs live long, comfortable lives with a heart murmur, especially when it is mild and monitored. The outlook depends on the underlying cause and stage, so your veterinarian is the best person to assess your dog and set a monitoring schedule.
Does a louder heart murmur mean my dog is sicker?
Not necessarily. The grade from 1 to 6 describes how loud the murmur is, not how well the heart is pumping. A dog with a loud murmur can feel well for a long time, which is why your veterinarian uses imaging and other tests to judge severity.
What food is best for a dog with a heart murmur?
There is no single best food for every dog with a heart murmur, because the right diet depends on the cause and any other conditions. Your veterinarian may recommend watching sodium and keeping your dog at a healthy weight, so ask them for specific diet guidance for your dog.
Is HeartRx a supplement I can buy for my dog's murmur?
No. HeartRx is a prescription heart medicine (pimobendan), not a supplement, so your veterinarian decides whether it fits your dog and how it is given. Follow the pack label and your vet's directions rather than starting it on your own.
How often should my dog's heart be rechecked?
Recheck frequency varies with the cause and severity of the heart condition, so there is no one-size-fits-all interval. Your veterinarian will set a schedule and may ask you to monitor resting breathing rate and energy at home between visits.
Taking the next step for your dog's heart
A heart murmur can feel worrying at first, but with steady monitoring and a plan built around your individual dog, many pets stay happy and active for a long time. If you would like to understand the care and treatment options available and how they fit alongside daily support, explore the heart health resources at RX Sciences and bring your questions to your own veterinarian. Together with your vet, you can choose the path that keeps your dog comfortable and well cared for.
