DogBreedCompass
← Back to breed profile

Myxomatous Mitral Valve Disease (MMVD) in Newfoundlands

Quick answer

Is this a Newfoundland condition?

No. Valve degeneration is characteristically a small-breed disease. This breed's documented cardiac issues are subaortic stenosis and dilated cardiomyopathy.

Small dogs wear out a valve. Giant dogs wear out a muscle. Both produce a failing heart, and almost nothing else about them is the same.

Myxomatous Mitral Valve Disease (MMVD) in Newfoundlands infographic

For Newfoundland owners who have encountered this diagnosis name and want to understand whether it applies, and for anyone comparing what they have read about their neighbour's spaniel with what their own vet is saying.

Important reminder

This guide is not medical advice. If your dog shows pain, sudden behavior change, or worsening symptoms, consult a licensed veterinarian.

Some links may be affiliate links. We may earn a commission at no extra cost to you. We only suggest products we believe are helpful for dog owners.

What this problem looks like

Myxomatous mitral valve disease is a degenerative thickening of the valve between the left atrium and left ventricle, causing blood to leak backwards and eventually producing congestive failure. It is the most common canine heart disease overall but is overwhelmingly a small and toy breed condition. In the Newfoundland, cardiac disease follows a different route entirely, through the documented conditions of subaortic stenosis and dilated cardiomyopathy.

Common triggers

  • Age-related degeneration of valve leaflets, typically in small-breed dogs
  • Progressive enlargement of the left atrium as leaking volume increases
  • In giant breeds, weakening of the heart muscle rather than the valve
  • A congenital narrowing below the aortic valve, documented in this breed
  • Excess body weight increasing the work a compromised heart must do
  • Heat and exertion raising cardiac demand in a heavily coated giant dog

Valve degeneration is not among the Newfoundland's documented health issues. Its relevance to this breed is comparative: understanding how small-breed valve disease behaves clarifies why the advice a Newfoundland owner needs is different, particularly regarding murmurs, monitoring and collapse risk.

Why this happens

Breed factors

Body size determines which cardiac disease a dog is likely to get, and the Newfoundland sits firmly at the giant end. At 100 to 150 pounds and 26 to 28 inches, the heart must supply an enormous mass of tissue, and it is muscle failure rather than valve degeneration that characterises this end of the size range. The breed's documented cardiac issues are subaortic stenosis, a structural defect present from birth, and dilated cardiomyopathy, an acquired weakening of the heart wall. A calm dog rated 2 out of 5 for energy provides its owner with little natural stress testing, so declining cardiac output goes unnoticed longer than it would in an athletic breed, and a nine to ten year lifespan compresses the whole timeline.

Environment factors

Whatever the underlying cardiac disease, the same environmental factors add load. Heat is the largest, because cooling requires increased cardiac output and a heavy water-resistant double coat makes cooling inefficient. Excess body weight, easy to accumulate in a calm breed, means more tissue for a compromised pump to supply. Sudden unconditioned exertion, stressful transport and warm indoor temperatures all raise demand. Households that measure food by scoop rather than by scale are, without intending to, adjusting their dog's cardiac workload upward.

What you can do at home (once it is not an emergency)

When to talk to your vet

Go the same day for any collapse or fainting episode, for breathing that stays laboured while the dog is resting, for gums that look pale, grey or bluish, or for an abdomen that swells over hours. In this breed a dog that faints during or after exertion should be treated as urgent rather than as a curiosity. Contact the clinic promptly, without waiting for a scheduled recheck, for a persistent new cough, a resting breathing rate that has risen and stayed up, unexplained weight loss, or a clear reduction in exercise tolerance. Ask for cardiac assessment before any planned anaesthetic.

At home, alongside your vet's plan

  • Count sleeping breaths per minute several times a week and write the number down with the date.
  • Ask for the specific diagnosis in writing, including what the imaging measured, rather than accepting a general description.
  • Keep a copy of the cardiac report accessible, so an emergency clinic that has never met your dog starts informed.
  • Log any episode of weakness, wobbliness or fainting with the date and the activity that preceded it.
  • Weigh your dog monthly and hold it at a lean body condition.
  • Move exercise to cool parts of the day and keep it steady rather than variable.
  • Check the assumptions in any cardiac advice you read online against whether it was written for small breeds.

More Newfoundland health & behavior issues

See all Newfoundland health problems, which breeds are prone to myxomatous mitral valve disease mmvd, or the full Newfoundland breed guide for temperament, exercise needs and ownership costs.

What to expect, and how you know it is working

Small-breed valve disease typically unfolds over many years, with long stable periods. Giant-breed cardiac disease generally moves faster, which is the practical reason the distinction matters. A Newfoundland with a cardiac diagnosis should expect an initial cluster of appointments while the picture is established, then rechecks measured in months rather than years. Owners who have absorbed a small-breed timeline are often unprepared for how quickly a giant-breed dog can change.

Success starts with an accurate name for the problem. Beyond that it means monitoring intervals that match a giant breed rather than a spaniel, a household that recognises collapse as urgent rather than odd, a stable sleeping respiratory log, and a dog that remains comfortable and engaged for as long as its heart allows. It does not mean a normal echocardiogram, and it does not mean the long slow decline that small-breed cardiology describes.

What Happens to a Degenerating Mitral Valve

The mitral valve sits between the left atrium and the left ventricle and stops blood flowing backwards when the ventricle contracts. It is a thin, flexible structure held in place by fine cords.

In myxomatous degeneration the valve leaflets thicken, become nodular, and lose the crisp edges that allow them to seal. Instead of closing cleanly, they leak. Every time the ventricle squeezes, some blood is pushed backwards into the atrium instead of forwards into the body.

That backward jet is what produces a murmur, heard loudest over the left side of the chest. Over years the leaking volume grows, the left atrium stretches to accommodate it, and eventually pressure backs up into the lungs, producing fluid accumulation and the cough and breathlessness of congestive failure.

The important detail is who this happens to. Degenerative valve disease is overwhelmingly a disease of small and toy breeds, typically appearing in middle age and progressing slowly over many years. Its prominence in canine cardiology reflects how many small dogs there are, not how universal the disease is.

Giant breeds do not follow this pattern. Their characteristic cardiac failure is muscular rather than valvular, and that difference changes the monitoring, the timeline and the prognosis.

Mitral Valve Disease in Newfoundlands - What Happens to a Degenerating Valve
Mitral Valve Disease in Newfoundlands - What Happens to a Degenerating Valve

How the Giant-Breed Cardiac Pattern Differs

The two documented cardiac conditions in this breed are subaortic stenosis and dilated cardiomyopathy. Neither behaves like the valve disease that dominates general canine cardiology writing.

  • The primary problem is muscle, not valve. Dilated cardiomyopathy weakens the heart wall so the chambers stretch and the pump ejects less with each beat.
  • It can be silent early. A weakening muscle may produce no murmur at all, so a clear stethoscope exam does not exclude it, whereas valve disease announces itself audibly.
  • Ultrasound is the diagnostic tool, not listening, because chamber size and contraction strength are the things being measured.
  • Rhythm disturbances matter far more. Abnormal electrical beats accompany muscle disease and carry a risk of collapse and sudden death, which is rare in early valve disease.
  • Progression tends to be faster. Small dogs often carry valve disease for many years; giant-breed muscle disease commonly moves on a shorter timeline.
  • The Newfoundland also carries a documented congenital defect, subaortic stenosis, which produces a left-sided murmur in a young dog and is not degenerative at all.
  • Any murmur in this breed therefore needs imaging to say which of these it is, rather than being assumed to be the common canine diagnosis.

Why the Distinction Changes What Owners Should Do

If a Newfoundland owner assumes valve disease, several things follow that are wrong for their dog.

They will assume a murmur is required for a heart problem to exist, and take a clear listening exam as reassurance. For muscle disease that reassurance is unfounded, and it is one of the more consequential misunderstandings in giant-breed ownership.

They will assume a long, slow decline with years of stable monitoring, and may not press for the earlier and more frequent imaging that a giant breed warrants.

They will underweight rhythm. Fainting, collapse or sudden weakness in a small dog with early valve disease is uncommon; in a giant dog with muscle disease it is one of the signs that most urgently needs reporting, because the electrical instability behind it can be fatal.

And they may be unprepared for how quickly the picture can change. A giant-breed dog can move from apparently well to seriously affected over a shorter period than small-breed cardiology prepares owners for.

The corrective is simple. Ask the veterinarian which specific condition your dog has, not which category, and ask what imaging showed rather than what was heard.

Reassured by the Wrong Textbook

Callum's Newfoundland, Iona, was six and had been listened to at every annual visit. Callum's mother had a cavalier with a well-managed valve problem, and he had absorbed a great deal from her experience: that heart disease announces itself as a murmur, that a murmur means years of gradual change, and that a clear chest is good news. Iona had never had a murmur. What she had, over one autumn, was a tendency to lie down partway through the evening walk and a habit of choosing the coolest room in the house and staying there. Callum put it down to a dog that had never been energetic getting a little older. He mentioned it at her annual visit almost in passing. The veterinarian listened, found nothing, and then said the thing that changed the year: in a giant breed, a normal listening exam does not settle the question. Iona's ultrasound showed an enlarged, poorly contracting left ventricle. She started treatment that month and is still doing well two years later. Callum's summary is blunt: everything he thought he knew about dog hearts, he had learned from a dog weighing eighteen pounds.

Key takeaway: Canine cardiology advice is written mostly about small dogs. In a Newfoundland, the absence of a murmur is not evidence of a healthy heart, and assuming otherwise costs time that a giant-breed diagnosis does not have to spare.

Frequently asked questions

Do Newfoundlands get mitral valve disease?

Degenerative mitral valve disease is characteristically a small and toy breed condition. It is not among the Newfoundland's documented cardiac issues, which are subaortic stenosis and dilated cardiomyopathy. Valve changes can occur in any dog, but they are not the expected pattern here.

My Newfoundland has a left-sided murmur. What is it likely to be?

In a young dog it raises the possibility of subaortic stenosis, a congenital narrowing below the aortic valve documented in this breed. In an older dog, changes associated with heart muscle disease are more likely. An ultrasound is what distinguishes them.

Why does my vet want an ultrasound when the murmur is quiet?

Because loudness is a poor guide to severity, and because the cardiac diseases documented in this breed are not reliably characterised by listening alone. Imaging measures chamber size, wall thickness, contraction strength and flow speed.

Can a Newfoundland have heart disease with no murmur at all?

Yes, and this is the single most important point on this page. Early dilated cardiomyopathy can be entirely silent to a stethoscope, so a normal listening exam does not rule out serious cardiac disease in a giant breed.

Is treatment the same for both types of disease?

There is overlap in supporting a failing heart, but the underlying problems differ and so do the specifics, including how much attention is paid to rhythm. Treatment decisions belong to a veterinarian who has seen your dog's imaging.

What home monitoring applies regardless of the diagnosis?

Counting sleeping respiratory rate over a full minute, several times a week, and recording it. A rising trend is one of the earliest home-detectable signs of a heart falling behind, whichever disease is responsible.

Should I still read general canine cardiology advice?

Read it critically. Most of it is written around small-breed valve disease because that is what most dogs have. Check whether what you are reading assumes a murmur, a slow timeline and a low collapse risk, because none of those assumptions transfer well to a giant breed.

Quick answers

View more answers
Health

Is this a Newfoundland condition?

No. Valve degeneration is characteristically a small-breed disease. This breed's documented cardiac issues are subaortic stenosis and dilated cardiomyopathy.

Health

Does a clear stethoscope exam mean a healthy heart?

Not in a giant breed. Early heart muscle disease can be completely silent, which is why ultrasound matters here.

Health

What should I ask after a cardiac exam?

Which specific condition, not which category, and what the imaging measured rather than what was heard.

Health

Why does collapse matter more in this breed?

Because rhythm disturbances accompany muscle disease and can be dangerous. Any fainting episode needs reporting the same day.

Health

What is the useful home measurement?

Sleeping breaths per minute, counted for a full minute and logged. The trend is what a cardiologist wants.

Related DogBreedCompass guides

  • Newfoundland dilated cardiomyopathy – Dilated cardiomyopathy is the muscle disease that actually affects this breed.
  • Newfoundland heart problems and subaortic stenosis – Subaortic stenosis is the breed's documented congenital defect.
  • Newfoundland heart murmurs – Understanding what a murmur does and does not mean is central here.
  • ventricular arrhythmias in Newfoundlands – Rhythm disturbances are the giant-breed cardiac risk owners underweight.
  • Newfoundland cardiac screening – The screening framework explains where each cardiac test fits.

Bring the right questions to the vet

A one-page prep sheet for this condition: the signs, the questions to ask, what to get priced. Unlocks here.

You get: Vet visit prep sheet

No spam. One-click unsubscribe. See our privacy policy.

Preview page 1 before you decide.

Related guides

Comparison
Newfoundland vs Welsh Springer Spaniel: Size, Cost & Temperament thumbnail

Newfoundland vs Welsh Springer Spaniel: Size, Cost & Temperament

ComparisonRead guide->
Comparison
Newfoundland vs Weimaraner: Size, Shedding, Cost & Temperament thumbnail

Newfoundland vs Weimaraner: Size, Shedding, Cost & Temperament

ComparisonRead guide->
Comparison
Newfoundland vs Rottweiler Mix: Size, Cost & Temperament Compared thumbnail

Newfoundland vs Rottweiler Mix: Size, Cost & Temperament Compared

ComparisonRead guide->
Comparison
Newfoundland vs Old English Sheepdog: Size, Cost & Temperament thumbnail

Newfoundland vs Old English Sheepdog: Size, Cost & Temperament

ComparisonRead guide->
Comparison
Newfoundland vs Shetland Sheepdog: Size, Cost & Temperament thumbnail

Newfoundland vs Shetland Sheepdog: Size, Cost & Temperament

ComparisonRead guide->
Comparison
English Springer Spaniel vs Newfoundland: Full Breed Comparison thumbnail

English Springer Spaniel vs Newfoundland: Full Breed Comparison

ComparisonRead guide->