What Is Degenerative Valvular Disease?

Degenerative valvular disease – commonly called mitral valve disease (MVD) – is the most common heart condition in dogs. It involves the gradual degeneration of one or more heart valves, most often the mitral valve, which separates the left atrium (upper chamber) from the left ventricle (lower chamber).

The tricuspid valve, located on the right side of the heart, may also be affected, though this is usually less severe.

In a healthy heart, valves close tightly to prevent blood from flowing backward. With degenerative valve disease, the valve tissue becomes thickened and may bulge backward (a process known as valve prolapse). This allows blood to leak in the wrong direction, creating turbulence that can be heard during examination as a heart murmur.

Over time, this leakage causes the heart chambers, particularly the left atrium and ventricle, to enlarge. As the disease progresses, blood flow through the heart becomes less efficient and fluid may begin to leak into the lungs (pulmonary oedema) or other tissues. When this occurs, the dog is said to be in congestive heart failure.

Which Dogs Are Affected?

Degenerative valvular disease is most commonly seen in:

  • Small‑breed, middle‑aged to older dogs, especially
    • Cavalier King Charles Spaniels
    • Chihuahuas
  • Other predisposed breeds, including
    • Whippets
    • Dachshunds
    • Terrier breeds
  • Some larger breeds, such as
    • Spaniels
    • Border Collies
    • German Shepherds
    • Labrador Retrievers

Common Clinical Signs

Dogs with mitral valve disease may show:

  • Reduced exercise tolerance, tiring more easily, or collapsing after exertion
  • Coughing or breathlessness, often worse at night or early in the morning
  • Reduced appetite, weight loss, or increased thirst

These signs often develop gradually and may worsen as the disease progresses.

How Is Degenerative Valvular Disease Diagnosed?

A heart murmur in a predisposed breed may raise suspicion, but murmurs can have many causes. Further testing is needed to confirm the diagnosis and assess disease severity.

Echocardiography (Heart Ultrasound)

This is the gold standard diagnostic test for valve disease. It allows real‑time assessment of:

  • Heart chamber size
  • Valve structure and movement
  • The presence and severity of valve leakage (using colour Doppler)

Echocardiography is painless and non‑invasive, requiring only a small patch of hair to be clipped.

NT proBNP Blood Test

This blood test can be a useful screening tool:

  • High levels suggest the heart is under strain and may be enlarged

Normal levels make severe enlargement less likely, although an ultrasound may still be recommended to determine the cause of a murmur.

Electrocardiogram (ECG)

An ECG assesses the heart’s electrical activity and rhythm. In some cases, a Holter monitor may be used for 24‑hour monitoring, particularly if symptoms occur at home rather than in the clinic.

Radiographs (X rays)

X‑rays are used to detect fluid build‑up in the lungs and to assess for other lung disease.

Can Degenerative Valvular Disease Be Treated?

Degenerative valvular disease is usually slowly progressive, often developing over many years.

Dogs Without Heart Enlargement

There is currently no evidence that early treatment improves outcomes before heart enlargement is detected on ultrasound.

Dogs With Heart Enlargement
(Pre‑Clinical Stage)

Once enlargement has been confirmed by echocardiography, the medication pimobendan has been shown to:

  • Delay disease progression
  • Support heart function
  • Extend survival

Pimobendan should only be started once heart enlargement is documented.

Dogs With Congestive Heart Failure

Additional medications may be required, including:

  • Diuretics (e.g. furosemide, spironolactone) to remove excess fluid from the lungs or abdomen
    • Increased drinking and urination are expected
  • ACE inhibitors (e.g. benazepril) to improve circulation and support heart efficiency

Anti‑arrhythmic or rate‑control medications (such as digoxin, diltiazem, sotalol, or amiodarone) if abnormal heart rhythms are present.

Surgical Options

Mitral valve repair surgery, performed using open‑heart bypass techniques, is available at a small number of specialist centres worldwide. This is major surgery and can be costly, but may offer long‑term benefits for carefully selected patients. Please contact us if you would like to discuss whether this option may be suitable for your dog.

Can Dogs Be Screened for Mitral Valve Disease?

Because valve disease usually develops later in life, screening can be challenging and no genetic test is currently available. For Cavalier King Charles Spaniels, the Kennel Club and Veterinary Cardiovascular Society recommend a screening scheme involving:

  • Auscultation (listening to the heart with a stethoscope)
  • Echocardiography

This screening is recommended prior to breeding.

Monitoring Your Dog at Home

  • Dogs with mild disease and no symptoms can usually continue normal walks and do not require dietary changes.
  • Dogs with more advanced disease should still enjoy gentle exercise but must avoid over‑exertion. Offer rest breaks and carry water.
  • Monitoring your dog’s resting breathing rate while asleep is one of the most helpful ways to track disease progression.
    • Fewer than 30 breaths per minute is ideal
    • Consistently higher rates should be reported to your veterinarian

Apps such as Cardalis can help record and track breathing rates over time.

Seek Immediate Veterinary Attention If Your Dog Develops:

Seek Immediate Veterinary Attention If Your Dog Develops:

  • Sudden difficulty breathing
  • Persistent or worsening coughing
  • Pale or blue gums or tongue
  • Fainting or collapse
  • Restlessness or distress

Your veterinarian can stabilise your dog and, if needed, consult with our cardiology team for further guidance.

Our veterinary hospital in Artarmon, Sydney is open 24 hours a day, 7 days a week. In an emergency, please call us on (02) 9436 4884.