Mitral valve disease in dogs is a progressive heart condition in which a valve on the left side of the heart becomes damaged and allows blood to leak backwards. It is particularly common in older, small-breed dogs. Many affected dogs remain comfortable and symptom-free for years, while others eventually develop heart enlargement and congestive heart failure.
Being told that your dog has a heart murmur or mitral valve disease can be frightening, especially when they still seem perfectly healthy. However, a diagnosis does not automatically mean heart failure is present or that your dog has a poor prognosis.
This guide explains the symptoms, causes, inherited risks, susceptible breeds, stages, treatment options and long-term outlook for dogs with mitral valve disease.
What Is Mitral Valve Disease in Dogs?
The heart contains four chambers and several valves that keep blood flowing in the correct direction.
The mitral valve sits between the left atrium and left ventricle. Its job is to prevent blood flowing backwards when the heart contracts.
In degenerative mitral valve disease, the valve gradually becomes thickened and changes shape. It may no longer close tightly, allowing some blood to leak backwards into the left atrium.
This leakage is called mitral regurgitation and often produces a heart murmur that a vet can hear with a stethoscope.
As leakage becomes more significant, the heart may enlarge to accommodate the additional blood volume. Eventually, pressure can build up in the blood vessels supplying the lungs, potentially causing fluid accumulation and congestive heart failure.
The condition is also called myxomatous mitral valve disease, or MMVD.
What Are the Early Symptoms of Mitral Valve Disease in Dogs?
Many dogs with early mitral valve disease show no visible symptoms. The first sign is often a heart murmur detected during a routine veterinary examination.
As the condition progresses, changes may become noticeable.
Early Signs Owners May Notice
Possible symptoms include:
- Reduced stamina during walks.
- Becoming tired more easily than usual.
- Reluctance to exercise or play.
- Coughing, particularly during rest or at night.
- Faster breathing while sleeping.
- Unusual tiredness or reduced enthusiasm for normal activities.
These symptoms are not specific to mitral valve disease. Coughing may result from airway problems, while reduced activity can have many causes.
What Are the Signs of Advanced Heart Disease?
Dogs developing congestive heart failure may experience persistent rapid breathing, increased breathing effort, weakness and reduced exercise tolerance.
Some dogs become restless because lying down makes breathing more difficult.
Fainting or collapse can occur in certain cases, although these symptoms may also indicate abnormal heart rhythms or other serious conditions.
Laboured breathing, collapse or blue-tinged gums require immediate emergency veterinary attention.
What Causes Mitral Valve Disease in Dogs?
The most common form is degenerative mitral valve disease, which develops as the valve's connective tissue gradually changes.
Healthy valve leaflets are thin and flexible. With degeneration, their structure becomes altered, reducing their ability to close properly.
Age-Related Degeneration
The condition becomes increasingly common with age, particularly in small dogs.
However, ageing is not the only factor, and some genetically susceptible dogs develop valve changes relatively early in life.
Breed and Genetic Susceptibility
Inherited characteristics appear to influence how early disease develops and how frequently it occurs in certain breeds.
Is Mitral Valve Disease Caused by Diet or Exercise?
Ordinary diet and exercise are not considered direct causes of degenerative mitral valve disease.
Maintaining a healthy body condition and appropriate fitness supports general health, but these measures cannot reverse structural valve degeneration.
Is Mitral Valve Disease Hereditary in Dogs?
Yes. Degenerative mitral valve disease has a strong inherited component in some breeds, particularly Cavalier King Charles Spaniels and Dachshunds.
However, inheritance is complex. Multiple genes and other factors appear to influence susceptibility and disease progression.
There is no single genetic test that reliably predicts the condition in every dog.
Responsible breeding programmes may use veterinary heart examinations and specialist cardiac screening to help reduce the risk of passing on inherited susceptibility.
Having a genetic predisposition does not mean every dog will develop severe disease or heart failure.
Which Dog Breeds Are Most Prone to Mitral Valve Disease?
Mitral valve disease can affect any dog, but it is particularly associated with smaller breeds.
Cavalier King Charles Spaniels
Cavaliers have one of the strongest recognised predispositions to degenerative mitral valve disease.
Valve changes and heart murmurs may develop at a younger age than in many other breeds, making appropriate cardiac screening especially important.
Dachshunds
Dachshunds are another breed with recognised inherited susceptibility.
As they age, regular veterinary examinations can help identify changes in heart sounds before obvious symptoms develop.
Our guide to when a Dachshund becomes a senior dog
Chihuahuas and Toy Poodles
Chihuahuas, Toy Poodles and other small breeds can develop degenerative valve disease, particularly during their middle and senior years.
Other Susceptible Breeds
Miniature Schnauzers, Yorkshire Terriers and other small dogs may also be affected.
Breed susceptibility indicates increased risk, not certainty. Diagnosis and treatment should always be based on the individual dog.
What Are the Stages of Mitral Valve Disease in Dogs?
Veterinary cardiologists commonly use a staging system developed by the American College of Veterinary Internal Medicine, known as ACVIM.
The stages range from A, indicating increased risk without structural disease, to D, describing advanced heart failure that no longer responds adequately to standard treatment.
Stage A: At Risk
Dogs in stage A have recognised risk factors, such as belonging to a susceptible breed, but do not have detectable structural heart disease.
They generally require routine screening rather than medication.
Stage B1: Heart Disease Without Significant Enlargement
Stage B1 dogs have structural mitral valve disease but no signs of congestive heart failure.
The heart is either not enlarged or does not meet the criteria for treatment intended to delay heart failure.
Medication is not routinely recommended at this stage, although monitoring is important.
Stage B2: Heart Enlargement Without Heart Failure
Stage B2 dogs still have no clinical signs of heart failure, but valve leakage has caused sufficient heart enlargement to meet established treatment criteria.
Appropriately selected dogs benefit from pimobendan, a prescription medication shown to delay the onset of congestive heart failure.
Stage C: Current or Previous Heart Failure
Stage C describes dogs that have developed clinical signs of congestive heart failure, including those whose symptoms are now controlled with medication.
Treatment commonly includes medication to improve heart function and reduce fluid accumulation.
Stage D: Advanced Heart Failure
Stage D describes heart failure that is no longer adequately controlled by standard treatment.
These dogs may need specialist medication adjustments, intensive monitoring or consideration of advanced interventions.
Mitral Valve Disease Stages and Treatment
The ACVIM consensus guidelines explain the evidence supporting this staging system and its treatment recommendations.
How Do Vets Diagnose Mitral Valve Disease in Dogs?
Diagnosis often begins when a vet hears a heart murmur during a routine examination.
However, a murmur alone cannot establish the disease stage or confirm whether the heart is enlarged.
Echocardiography
An echocardiogram is an ultrasound examination of the heart.
It allows the vet or veterinary cardiologist to assess valve movement, blood leakage, chamber size and heart function.
This is particularly valuable when deciding whether a dog meets stage B2 treatment criteria.
Chest X-rays
Chest X-rays can help assess heart size and identify fluid accumulation within the lungs.
They are especially useful when a dog develops coughing or breathing difficulties.
Other Investigations
Additional tests may include blood pressure measurement, electrocardiography, blood tests and cardiac biomarkers.
These investigations help assess the dog's overall health and identify conditions that could affect treatment.
Our guide to heart murmurs in dogs explains what different murmur grades mean and why further investigation may be recommended.
How Is Mitral Valve Disease Treated in Dogs?
Treatment depends on the stage of disease, the presence of heart enlargement and whether congestive heart failure has developed.
Monitoring Without Medication
Dogs with stage B1 disease generally do not need medication specifically for mitral valve disease.
Regular examinations and repeat imaging help identify progression and determine when treatment becomes appropriate.
Pimobendan for Stage B2 Disease
Pimobendan helps the heart pump more effectively and improves blood vessel function.
In dogs meeting established stage B2 criteria, it can delay the onset of congestive heart failure.
It is a prescription medicine and should only be started following veterinary assessment.
Diuretics and Heart Failure Medication
Dogs with congestive heart failure often require diuretics, such as furosemide, to reduce fluid accumulation in the lungs.
Other medicines may include pimobendan, spironolactone and selected drugs that influence blood pressure and the body's fluid-regulating systems.
Medication choices depend on the individual dog and require monitoring of kidney function, electrolytes and clinical response.
Can Surgery Repair the Mitral Valve?
Specialist surgical repair is possible in selected dogs at centres with appropriate expertise and facilities.
However, this is not widely available, involves substantial cost and requires careful assessment of the potential benefits and risks.
What Is the Life Expectancy of a Dog With Mitral Valve Disease?
Life expectancy varies considerably according to the disease stage, age, other medical conditions and response to treatment.
Positive Outcomes
Some dogs remain in the early stages for years without developing heart failure.
Dogs diagnosed at stage B2 may benefit from treatment that delays progression, allowing additional time with a good quality of life.
More Serious Outcomes
Dogs that develop congestive heart failure face a more guarded prognosis.
Some respond well to medication and remain comfortable for months or longer, while others deteriorate more rapidly.
Advanced disease may cause recurring fluid accumulation, abnormal heart rhythms, weakness and breathing difficulties.
There is no reliable single life expectancy figure for every affected dog. Your vet can provide a more meaningful prognosis based on examination and imaging results.
How Can You Care for a Dog With Mitral Valve Disease at Home?
Home care should complement the treatment and monitoring plan recommended by your vet.
Monitor Sleeping Breathing Rate
Counting your dog's breaths while they are genuinely asleep can help identify changes that may indicate developing heart failure.
One breath consists of the chest rising and falling once.
A sleeping respiratory rate below approximately 30 breaths per minute is common in stable dogs. A persistent increase above your dog's usual rate, particularly above 30, should prompt veterinary advice.
Breathing effort is just as important as the number. A dog struggling to breathe needs emergency care regardless of the rate.
Maintain Suitable Exercise
Many dogs with early or stable disease can continue enjoying regular walks.
Exercise should be adapted if your dog becomes unusually tired, coughs or shows breathing changes.
Avoid pushing an unwell dog to complete a walk.
Support Healthy Nutrition
Provide a complete, balanced diet and maintain a healthy body condition.
Dogs with heart failure may benefit from individual dietary adjustments, including appropriate sodium management.
Do not introduce severe salt restriction or supplements without veterinary advice.
No general pet supplement has been shown to repair a degenerating mitral valve or replace prescribed cardiac medication.
When Is Mitral Valve Disease an Emergency?
Seek emergency veterinary treatment if your dog develops laboured breathing, collapse, blue or very pale gums, or severe weakness.
Rapid breathing accompanied by increased effort, particularly when your dog is resting, may indicate fluid accumulation in the lungs.
Do not wait until the next routine appointment if your dog is struggling to breathe.
For other symptoms that require urgent attention, read our guide to common medical conditions in dogs and their warning signs.
Frequently Asked Questions About Mitral Valve Disease in Dogs
Can a Dog Live a Normal Life With Mitral Valve Disease?
Yes. Many dogs with early disease remain comfortable and active for years. Regular monitoring helps identify when treatment is needed.
Does a Heart Murmur Mean My Dog Has Mitral Valve Disease?
No. Mitral valve disease is a common cause of heart murmurs, particularly in older small dogs, but murmurs can have other causes. An echocardiogram can help establish the diagnosis.
Can Mitral Valve Disease Be Cured?
Medication cannot reverse degenerative valve changes. Specialist surgical repair may be possible in selected cases, but most dogs are managed through monitoring and medication when appropriate.
Should Dogs With Mitral Valve Disease Still Go for Walks?
Many dogs with early or stable disease can continue regular walks. Activity should be adjusted according to symptoms and veterinary recommendations.
Does Every Dog With Mitral Valve Disease Need Medication?
No. Dogs with stage B1 disease are usually monitored without medication. Dogs meeting stage B2 criteria benefit from pimobendan, while dogs with heart failure need additional treatment.
Why Does My Dog Cough at Night?
Coughing can occur with advanced heart disease, but airway disorders are also common causes. A vet may recommend chest imaging and other investigations to identify the reason.
Can Mitral Valve Disease Cause Sudden Death?
Sudden death is possible with serious heart disease but is not the usual outcome for dogs with early mitral valve disease. Collapse, fainting or sudden breathing difficulties require urgent veterinary assessment.
Final Thoughts
Mitral valve disease in dogs is common, particularly in older small breeds, but a diagnosis does not automatically mean heart failure or a poor quality of life.
Many dogs remain comfortable for years, especially when the condition is identified early and monitored appropriately.
Understanding the disease stage, following veterinary recommendations and recognising changes in breathing or stamina can help you make informed decisions about your dog's care.
This article provides general educational information and does not replace individual veterinary diagnosis, treatment or emergency care.
