Mitral valve disease in dogs: stages, signs and care

Myxomatous mitral valve disease is a gradual degeneration of the valve between the left upper and lower chambers of a dog's heart. The changed valve no longer closes tightly, so some blood leaks backwards.

The leak may remain well compensated for years, but it can make the heart enlarge and eventually lead to fluid in the lungs. It is also called degenerative mitral valve disease or MMVD. [1]

The mitral valve acts like a one-way door between the left atrium and left ventricle. It opens for blood moving into the ventricle and closes when the ventricle pumps.

A healthy seal directs blood forwards around the body. When the valve edges become thickened or distorted, part of each heartbeat can instead push blood backwards into the atrium. [2]

No. A murmur is the sound of turbulent blood flow, while mitral valve disease is one possible cause. In MMVD, blood leaking through the changed valve commonly creates a left-sided systolic murmur.

Other heart conditions can also cause murmurs, and a quiet murmur does not prove a healthy heart. Examination and imaging establish what is causing the sound and how the heart has responded. [1]

Stage A means risk without structural disease; stage B means structural disease without heart-failure signs; stage C means current or previous heart failure; and stage D means heart failure that is difficult to control with standard care.

Stage B is divided into B1 and B2 according to cardiac remodelling. The staging system links current disease status to evidence-based monitoring and management rather than simply ranking a murmur. [3]

Yes. Many dogs have a murmur and structural valve disease long before they show heart-failure symptoms. Some never reach congestive heart failure during their lifetime.

This symptom-free period still includes different stages. Heart-size measurements separate earlier B1 disease from B2 disease, where enlargement changes the evidence-based management discussion. [1]

The precise trigger is not known. The valve's supporting tissue gradually changes, thickens and weakens, preventing the leaflets from meeting properly when the heart contracts.

Age and inherited susceptibility are important, especially in some small breeds. Ordinary exercise, excitement or a single dietary choice does not explain this chronic degenerative process. [1]

MMVD is seen most often in older, smaller dogs, although any size can be affected. Cavalier King Charles Spaniels develop it particularly commonly and often at a younger age.

Breed raises risk but does not predict an individual dog's stage or future. A murmur-free predisposed dog and an affected dog with enlargement need very different follow-up. [3]

No. MMVD is progressive, but the pace varies greatly. Many dogs remain stable without symptoms for a long time, while a smaller group develops heart enlargement and later congestive heart failure.

One examination cannot provide a timetable. Changes in heart size, breathing, exercise tolerance and other findings over time are more informative than the diagnosis label alone. [3]

Advanced MMVD can cause faster or harder breathing, reduced stamina, restlessness, coughing, weakness or fainting. Appetite and body weight may also decline when heart failure becomes chronic.

These signs are not specific to the heart, especially in older dogs. Lung, airway, kidney and other illnesses can look similar, so a new symptom needs assessment rather than automatic attribution to a known murmur. [1]

Not necessarily. Older small dogs commonly have airway disease as well as MMVD, and either can cause coughing. A murmur plus a cough does not by itself prove fluid in the lungs.

The pattern of breathing, examination, chest X-rays and sometimes ultrasound or blood markers help separate heart failure from airway disease. A changing cough still deserves review. [3]

A sustained rise above a dog's usual sleeping or resting breathing rate can be an early sign that congestion is worsening. The trend is more useful than an isolated count after activity, heat or stress.

The veterinary team can explain how to count and what change should trigger contact for that dog. Laboured breathing matters even when a numerical count is unavailable. [3]

Struggling to breathe, blue or grey gums, collapse, coughing froth or being unable to settle because of breathlessness is an emergency. Contact an emergency veterinary service immediately and minimise stress during transport.

These signs can occur when fluid severely interferes with oxygen exchange, but other life-threatening problems can look similar. Home medication changes are not a substitute for urgent examination. [3]

Yes, fainting can occur, but it is not specific to MMVD. Abnormal rhythms, pulmonary hypertension, airway problems and non-cardiac causes can also cause collapse or apparent fainting.

A collapse episode warrants prompt veterinary assessment, especially if repeated, prolonged or accompanied by breathing difficulty. A video and description of recovery can help distinguish fainting from a seizure. [1]

The vet considers the murmur's location and character alongside age, breed, pulse, breathing and symptoms. Further testing may be suggested to identify the cause and measure heart enlargement.

A murmur grade records sound intensity, not the full disease stage. Baseline imaging can be valuable because later comparisons show whether the heart is changing. [3]

An echocardiogram shows the mitral valve moving, the backward blood flow and the sizes and function of the heart chambers. It can confirm MMVD and identify important enlargement or another heart condition.

Measurements are interpreted together rather than from one image. The examination also helps separate B1 from B2 disease and plan appropriate monitoring or treatment. [1]

Chest X-rays show overall heart size and, crucially, whether fluid is present in the lungs. They also reveal airway or lung changes that may explain coughing or breathlessness.

X-rays do not show valve leaflets as an ultrasound does. A baseline image and later comparison can help track enlargement and distinguish compensated disease from congestive heart failure. [1]

No single blood test diagnoses heart failure on its own. NT-proBNP can add useful evidence about cardiac strain, especially when the clinical picture could be heart or lung disease.

Routine blood and urine tests also assess kidneys, electrolytes and other illnesses before and during treatment. Results are interpreted with examination and imaging, not used as a standalone verdict. [3]

The diagnosis combines symptoms and examination with evidence that pressure from the leaking valve has caused fluid in the lungs. Chest X-rays are commonly central, with ultrasound and other tests adding context.

A cough alone is insufficient because airway disease is common in the same dogs. The vet also assesses kidney function and other illness before selecting a treatment plan. [3]

For dogs that meet stage B2 enlargement criteria, pimobendan can delay the onset of congestive heart failure. It is not prescribed merely because any murmur is present.

The supporting trial studied a defined group with confirmed MMVD and cardiac enlargement. A vet checks that the dog matches the clinical criteria and selects the prescription and monitoring plan. [4]

Management aims to remove excess fluid, support forward blood flow, control harmful hormonal responses and keep the dog comfortable. Several prescription medicines are commonly combined once heart failure has occurred.

The exact combination changes with kidney function, blood pressure, symptoms and response. Acute breathing distress needs hospital care; stable home treatment still requires examinations and blood monitoring rather than fixed lifelong doses. [3]

Monitoring may include clinical examination, breathing and symptom history, chest X-rays, echocardiography, blood pressure and laboratory tests. The mix and interval depend on stage and rate of change.

At home, appetite, weight, activity, medication tolerance and resting breathing trends provide useful context. A new symptom can justify an earlier check rather than waiting for the planned appointment. [3]

Count when the dog is asleep or quietly resting and learn that individual's usual pattern with guidance from the veterinary team. Record trends alongside effort, coughing and comfort.

Heat, dreaming, stress and recent activity can alter an isolated count. A sustained rise or any laboured breathing warrants contact according to the dog's plan; obvious distress is an emergency regardless of the number. [3]

Many symptom-free dogs can continue comfortable regular activity, while dogs with heart failure may need gentler, self-paced exercise. The suitable level depends on stage, breathing and individual tolerance.

Exercise is stopped and veterinary advice sought if it brings unusual breathlessness, weakness or collapse. Maintaining enjoyment and muscle matters, but forced exertion is not a test of cardiac fitness. [3]

There is no single diet for every stage of MMVD. Maintaining a healthy body condition, appetite and adequate nutrition is important, while advanced heart failure can create more specific nutritional concerns.

Abrupt restriction or unreviewed supplements can be unhelpful, especially with kidney disease or poor appetite. The vet can align food choices with stage, medicines, blood results and the dog's willingness to eat. [3]

Outlook varies widely. Many dogs remain symptom-free for years, whereas heart failure shortens life and requires ongoing treatment. Stage, heart enlargement, kidney health and response all matter.

A population median cannot forecast one dog. The most useful discussion combines current stage with changes over time, comfort, treatment options and the dog's other health conditions. [1]

Yes. Most progression is gradual, but rupture of a supporting valve chord can abruptly increase leakage and cause severe breathing difficulty. Rhythm problems or another illness can also destabilise a previously compensated dog.

A sudden major change needs urgent veterinary assessment, and breathing distress is an emergency. It should not be managed by waiting for the next routine heart check. [1]

Yes. MMVD has an inherited component in some breeds, so age at murmur onset, specialist findings and family history can be relevant when selecting breeding dogs. Surgery does not remove inherited susceptibility.

Breed-specific heart schemes may define the appropriate examination and certification. Responsible decisions also consider other inherited disease and genetic diversity rather than relying on one auscultation result alone. [3]

Track breathing comfort, sleep, appetite, interest in family life, walking ability, medication tolerance and good versus difficult days. Small changes across several areas can matter more than one dramatic score.

The veterinary team can use that record alongside examination and tests to adjust care. Persistent distress, inability to rest or loss of valued activities calls for a frank reassessment of comfort and options. [3]