Mitral valve endocardiosis in dogs

12 September 2022 - 4 min read
Cavalier King Charles Spaniel being examined by a vet

Cardiac disease is a major player not only in human medicine, but also one we manage frequently in the veterinary world. We commonly see dogs with disease of the left atrioventricular valve, better known as the mitral valve.

While there are many things that can affect this heart valve including genetic defects, infections, and tumours, the main abnormality by far is endocardiosis.

Endocardiosis is the term used to describe thickening and irregularity of the valve. This can happen to any of the heart valves, though the mitral valve seems to have an affinity for developing this degenerative condition.

We’re going to break down into simple terms why exactly dogs with mitral valve disease have problems and how pet owners can best support their pups with cardiac disease.

A person high fiving a dog

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A person high fiving a dog

What actually is the mitral valve?

The mitral valve is the common term for the left atrioventricular valve, or the valve that controls blood flow between the left atrium and left ventricle of the heart.

There are four major valves in the hearts of dogs and cats, each of which controls blood flow between two areas. Blood should only flow in one direction.

These valves are very thin, leaflike structures with small little branches around their edges that attach them to the surrounding tissues. They open and close as the heart beats to allow blood to move through this one way system.

Four chambers make up the primary structure of the heart. There are two atria and two ventricles with a left and right of each.

Because the heart, lungs, and their surrounding vessels are such a refined system, irregularities of the valve shape or structure can have a major impact.

In cases of endocardiosis, the valve becomes nodular and thickened. This means it slowly loses its effective ability to keep the blood flow in the heart moving in the correct direction. As the valve shape becomes abnormal, small amounts of blood will leak backward.

It is this change to blood flow that causes the sound of a heart murmur (although heart murmurs can have lots of other causes, like anaemia).

Over time, the blood flow becomes so irregular that the heart itself can no longer pump fluid through as it needs to.

If this continues over time, this back-up of blood will lead to heart enlargement and then to fluid build-up in the lungs.

This step is known as congestive heart failure, and also causes other troubles like decreased ability to provide the body with the levels of oxygen it needs.

Which dogs get mitral valve endocardiosis?

Mitral valve endocardiosis is most commonly seen in these breeds:

We suspect the major contributor to developing mitral valve endocardiosis is genetic.

Small breeds appear to be most commonly affected, with the King Charles Cavalier Spaniel being significantly represented. ManyPets saw 227 claims for mitral valve disorder in 2021 and one-in-five of these claims were for Cavalier King Charles Spaniels.

Occasionally we can see cases in larger breeds such as German Shepherds and Labradors.

Symptoms of mitral valve disease

While it will take your veterinarian listening to your dog’s chest to hear the heart murmur in cases of mitral valve disease, there are also signs you can watch for at home.

Early on in the disease, there are often no clinical symptoms. In later stages, some of the common signs of progressive heart disease include:

  • Coughing

  • Difficulty breathing (increased respiratory effort)

  • Reluctance to exercise or trouble recovering from exercise

  • Decreased appetite or lack of appetite

  • Lethargy

  • Weakness

  • Collapse

Costs for pets with mitral valve disease

if your pet has mitral valve disease, there can be some immediate and ongoing costs to think about.

The diagnosis

Diagnosis of mitral valve disease truly relies on an echocardiogram, which is an ultrasound of the heart.

It can be heavily suspected based on the patient's age, clinical symptoms and abnormalities seen on radiographs (x-rays), however true diagnosis requires the more sophisticated imaging of an echocardiogram.

Initial costs are typically put towards blood tests, blood pressure, and imaging.

The medications

Patients with mitral valve disease will usually be put one at least one (but usually more) medications to help the heart continue to work more efficiently as disease progresses.

Medications can include:

  • Drugs to help the heart pump more effectively (positive inotropes like Pimobendan)

  • Drugs to help decrease the fluid load the heart has to deal with (diuretics like Furosemide and Spironolactone)

  • Drugs to help decrease fluid retained by the kidneys and decrease arterial blood pressure (ACE inhibitors like Enalapril and Benazepril)

These are consistently adjusted and monitored to maximise their effects without doing secondary harm to other body systems such as the kidneys.

The check ups

Patients receiving therapy for the management of mitral valve disease need regular monitoring by their vet. These visits will likely include blood tests to check organ function while taking long term medications and chest x-rays to look for signs of congestive heart failure.

If you can afford it, rechecks with a veterinary cardiologist are recommended, as they will be able to perform repeat echocardiograms.

Does pet insurance cover mitral valve disease?

If your dog’s covered by a dog insurance policy at the time they’re diagnosed, their diagnosis, medication and check ups for mitral valve disease should be covered.

All ManyPets pet insurance policies are lifetime insurance – that means that they’re particularly suitable for chromic conditions like heart disease as the vet fee limit will refresh each year when you renew.

Our MoneyBack option pays back 20% of your premium if you don't claim.

Life expectancy of dogs with mitral valve endocardiosis

It is true yes, dogs with cardiac disease live shorter lives than their counterparts without it.

That being said, pets with cardiac disease supported by medications can live many quality years before therapies cannot keep up with the loss of heart function.

Pets with mitral valve disease can have an increased risk of sudden death as well as increased risks under anaesthesia. How severely they’re affected may limit how your vet can treat them for this and other conditions.

Make sure you understand the treatment plan and prognosis from your vet and ask as many questions as you need to about their ongoing care.

Only you can know when your dog’s quality of life is so affected that you need to think about euthanasia, but work with your vet to look after their happiness until then.


Kirsten Ronngren DVM MRCVS
Veterinary surgeon

Veterinary surgeon Dr Kirsten Ronngren joined ManyPets in 2022. Alongside her extensive experience as a vet in small animal and feline-only clinics, Kirsten is passionate about online content creation. Kirsten’s a regular on ManyPets’ social media and video content with her no-nonsense attitude to keeping our customers’ pets happy and well.