If your vet has just told you they heard a heart murmur during your dog or cat’s check up, the first thing to know is this: a murmur is a finding, not a diagnosis. It is simply an extra sound the stethoscope picks up between or during the normal “lub dub” of the heartbeat, and it tells your vet that blood flow through the heart is turbulent somewhere.
What that turbulence means for your pet depends on where the murmur sits, how it behaves over time, and what turns up on further tests. This is where general practice and vet cardiology work together, and it is worth understanding how that handoff actually happens before you find yourself in the middle of it. At Pet Medical Milsons Point, this is a conversation we have with owners most weeks, so we have put together a plain language walkthrough of the grading scale and what happens next.
We wrote this piece because owners are routinely handed a grade number, a 2 out of 6 or a 4 out of 6, with very little explanation of what it changes practically. The grading scale is genuinely useful information, not just a technical detail for the file notes, and knowing what each band tends to mean can take a lot of the anxiety out of a diagnosis that, for many pets, turns out to be manageable for years.
What Is a Heart Murmur, and Why Did Your Vet Mention One?
A normal heartbeat makes two sounds as the heart valves close. A murmur is an additional whooshing or swishing sound caused by turbulent blood flow, usually because a valve is not closing as tightly as it should, or because blood is moving through a narrowed or abnormal opening.
Murmurs can be present from birth, in the case of some congenital defects, or they can develop later in life as valves degenerate with age, which is especially common in small breed dogs.
Not every murmur means disease is progressing, and not every murmur needs to be chased immediately. Some are what vets call innocent or physiologic, particularly in young, growing animals, and they resolve on their own.
Others are the first audible sign of a condition that will need monitoring for the rest of the pet’s life. The grade is one of several pieces of information your vet uses to decide which category your pet is likely in.
How Vets Grade a Heart Murmur, 1 to 6
The grading scale describes how loud the murmur is and how easily it can be heard, not how serious the underlying disease is.
A loud murmur can come from a relatively mild leak, and a quiet murmur can occasionally sit over a more significant problem. Grade is one input, not the whole answer, but it is a useful shorthand your vet will use consistently at every visit to track change over time.
Grades 1 to 2: Soft and Often Incidental
These are quiet murmurs that take a careful listen in a calm, quiet room to detect at all. In a young puppy or kitten, a grade 1 or 2 murmur is often innocent and may disappear by four to six months of age.
In an older pet, a soft murmur discovered for the first time is usually the trigger for a “let’s keep an eye on it” conversation rather than an immediate referral, with a recheck scheduled for three to six months later to see whether it has changed.
Grades 3 to 4: Moderate, Usually Worth Investigating Further
A murmur in this range is easy to hear without much effort and is less likely to be innocent, particularly if it is a new finding in an adult or senior pet.
This is generally where your general practice vet starts recommending baseline tests, and where a conversation about vet cardiology referral first comes up, especially if the pet also has other signs such as a reduced tolerance for exercise, a new cough, or faster breathing at rest.
Grades 5 to 6: Loud Murmurs That Rarely Wait
At this level, the murmur is loud, easy to hear, and in a grade 6 murmur can sometimes even be felt as a vibration through the chest wall.
Murmurs at this grade are taken seriously regardless of whether the pet is showing obvious symptoms, and they usually move fairly quickly to further diagnostic testing so that a management plan can be put in place before symptoms progress.
What Happens After a Murmur Is Detected: The General Practice Decision Pathway
This is the part owners are rarely walked through, so here is the pathway a general practice actually follows once a murmur is picked up, from the first appointment through to a possible specialist referral.
Step 1: History and Physical Exam
Your vet will ask about changes you may have noticed at home: coughing, tiring more easily on walks, reluctance to play, increased breathing rate at rest, or fainting episodes.
They will also check the murmur’s location on the chest, its timing in the heartbeat, and how it compares with any previous notes on file. A murmur that has been stable at grade 2 for three years tells a very different story to one that has jumped from grade 2 to grade 4 in six months.
Step 2: Baseline Tests at Your General Practice Vet
Depending on the grade and the history, your vet may recommend chest X-rays to look at heart size and the lungs, blood pressure measurement, and blood tests to check overall organ function before any medication is considered.
These baseline tests are usually done at the general practice level and give a reasonable picture of whether the heart is under strain.
Step 3: When a Referral for an Echocardiogram Makes Sense
An echocardiogram, a cardiac ultrasound, is the test that actually shows which valve or chamber is involved and how significant the abnormality is. It is a specialist skill, and it is the point where a general practice case genuinely benefits from vet cardiology input.
Referral is typically recommended when the murmur is grade 3 or louder, when it is a new or rapidly changing finding, when baseline tests suggest the heart is enlarging, or when your pet is showing clinical signs such as coughing, exercise intolerance or breathing changes.
A soft, stable, longstanding murmur with a healthy, active pet and normal baseline tests may reasonably be monitored at general practice level for longer before that step is taken.
Common Causes of Heart Murmurs in Dogs and Cats
Dogs
Small and large breed dogs tend to develop different underlying problems, which is part of why breed and age are among the first things a vet will factor in once a murmur is heard.
Degenerative Mitral Valve Disease
This is the most common cause in older, small breed dogs. The valve between the heart’s left chambers thins and leaks over time, and it is the reason breeds such as Cavalier King Charles Spaniels are monitored closely for murmurs from middle age onward.
Dilated Cardiomyopathy
In larger breeds, dilated cardiomyopathy, where the heart muscle itself weakens, is a more frequent underlying cause, and it can produce a murmur or, in some cases, none at all, which is one reason larger breeds are sometimes screened even without an obvious murmur present.
Congenital Defects
Congenital defects such as a patent ductus arteriosus are picked up in puppies, often on their very first vaccination visit, which is one reason a thorough chest listen is part of every puppy check even when nothing seems wrong at home.
Cats
Cats are a special case because murmurs are common and heart disease is easy to miss.
Hypertrophic Cardiomyopathy
A thickening of the heart muscle, hypertrophic cardiomyopathy is the most frequent cause of a murmur in cats and can be present with a very soft murmur, a loud one, or occasionally no murmur at all, which is part of why cats can go undiagnosed until a crisis occurs.
Any new murmur in a cat, however soft, is generally worth discussing with your vet, and blood pressure and thyroid checks are often recommended alongside a cardiac work up in middle aged and older cats.
Living With a Heart Murmur: What Owners Can Actually Do
A murmur diagnosis is not automatically a countdown clock. Many pets live full, comfortable lives for years with a monitored murmur, particularly when it is caught early and rechecked on a sensible schedule.
Practical things owners can do include: keep a simple diary of resting breathing rate, since a rising trend is one of the earliest warning signs vets look for; stick to recheck appointments even when your pet seems completely fine, because murmur grade and heart size can change gradually and silently; and mention any new symptom, however minor it seems, at the next visit rather than waiting for the annual check up. None of this requires specialist equipment at home, just consistency.
Frequently Asked Questions About Heart Murmurs in Pets
No. Grade describes loudness, not prognosis. Two pets with the same grade 3 murmur can have very different outlooks depending on the underlying cause, their age, and how the heart responds over time. That is exactly why further tests, not the grade alone, guide any long-term prognosis.
Some very soft murmurs can be harder to hear on some days than others depending on how relaxed or excited your pet is during the exam, and murmur grade can genuinely be affected by hydration, anxiety and heart rate at the time of listening. This is one reason your vet may listen again on a calmer day before making decisions based on a single reading.
A murmur itself is not painful. It is a sound, not a symptom your pet experiences directly. Any discomfort your pet may show relates to the underlying condition causing the murmur, if one develops, rather than the murmur itself.
Not necessarily. Whether a referral for an echocardiogram or other diagnostic imaging is recommended depends on grade, history, age and any baseline test findings, and your vet will talk you through the reasoning for your pet’s specific situation rather than applying a blanket rule.