Mitral Valve Disease in Dogs

By Laura Russell, DVM, MBA, DABVP on Jun. 21, 2023

What Is Mitral Valve Disease in Dogs?

To understand valve disease in dogs, think about the heart as a pump. The left side of the heart pumps freshly oxygenated blood from the lungs to the rest of the dog’s body. The mitral valve is a regulator of the blood flow between the two left chambers, the atrium, and the ventricle. When it is working correctly, the mitral valve prevents any backflow of blood from the ventricle back into the atrium when the heart muscle contracts.

With mitral valve disease the valve will not function as well, and some blood may leak in the wrong direction when the muscle contracts. A small amount of backflow is not an issue, but often, over time, the valve becomes thicker and stiffer and the volume of backflowing blood increases.

As a result, the heart becomes a less efficient pump. The heart muscle will try to compensate by getting thicker, which increases the overall size of the heart. In some dogs, mitral valve disease will progress enough so that fluid begins to accumulate in the lungs simply because the heart cannot keep up. Accumulation of the fluid in the lungs is known as pulmonary edema. Its presence indicates the dog is in congestive heart failure.

Two other names for mitral valve disease in dogs:

Degenerative mitral valve disease
Canine myxomatous mitral valve disease

Symptoms of Mitral Valve Disease in Dogs

Early in the disease, there will be no symptoms. In later stages, you may see:

Exercise intolerance (tires easily or after little effort)
Cough
Rapid breathing
Increased effort in breathing
Clear nasal discharge
Unable to rest comfortably, moving around
Decreased appetite

Causes of Mitral Valve Disease in Dogs

Mitral valve disease is a common condition that occurs in dogs, especially smaller-breed dogs as they age. Research has shown that 85% of small-breed dogs will have mitral valve disease by the time they reach 13.

Mitral valve disease is likely to have a genetic component because it is seen frequently in Cavalier King Charles Spaniels and Dachshunds, along with some terrier breeds.

How Veterinarians Diagnosis Valve Disease in Dogs

Physical exams help to evaluate the heart for murmurs, which are the earliest sign of mitral valve disease. Murmurs are detected and graded when your veterinarian listens to your dogs’s chest with a stethoscope.
Medical history is reviewed by your veterinarian to note any recent changes in breathing, cough, or differences in behavior that could indicate progressing mitral valve disease.
Radiographs (X-rays of the chest) are performed to check heart size and shape as well as evidence of fluid in the lungs.
NT ProBNP testing is done on blood samples to detect strain on the heart muscle. Elevations indicate mitral valve disease is present and severe enough to cause heart muscle changes.
Echocardiograms (ultrasounds of the heart): This diagnostic test, usually done by a veterinary cardiologist, shows the heart muscle and valves and measures heart function, and is considered the best way to diagnose mitral valve disease.
ECGs (electrocardiograms) check for arrythmias (abnormal electrical activity).
Blood pressure measurement: Done to check for high blood pressure.
Complete blood counts, chemistry panels, and urinalysis are lab tests done to monitor health, organ function, and kidney values. These tests are especially important if dogs are taking medications or if there are issues with blood pressure.

Mitral Valve Disease Stages

Veterinary cardiologists have created a classification system to categorize the severity and to mark progression of the disease.

Stage A: No disease noted yet, but dogs in this group are at high risk of developing the disease (breed-specific ).
Stage B1: Dogs in this stage have very minimal leakage of blood between the atrium and the ventricle, and mild enlargement of the heart muscle.
Stage B2: More leakage is present and the heart has grown significantly in size. This stage is usually when medications are prescribed.
Stage C: In this stage, dogs have congestive heart failure and require medications for treatment. Stage C pets are treated with standard medications doses, and depending on the severity, may require hospitalization with supplemental oxygen for initial treatment.
Stage D: In this stage, dogs have congestive heart failure and are not responding to standard doses of the medications needed to treat them. Very aggressive doses of medications are used, but often there is limited response. Dogs in Stage D require hospitalization for oxygen support and IV medications to try to improve their condition.

Treatment of Mitral Valve Disease in Dogs

Treatment is dependent on the stage of disease progression. Dogs in Stages A or B1 require monitoring, but usually no medication. Stages B2, C, and D require medication.

Medications:

Furosemide and torsemide: These medications are diuretics, which remove fluid from the body and minimize the ongoing work and stress on the heart.
Spironolactone: This is also a diuretic used to eliminate fluid. Spironolactone works in a different part of the kidney than furosemide, and they are often paired together in treatments to help maintain an electrolyte balance.
Benazepril and enalapril are angiotensin-converting enzyme inhibitor (ACEI) medications. They protect the kidneys from some of the secondary effects of heart disease and also control high blood pressure.
Pimobendan is a medication used to improve the strength and function of heart muscle.

Supportive care:

For dogs in acute congestive heart failure, hospitalization with supplemental oxygen and injectable medication is often needed to stabilize their condition.
Once they are stable on oral medication, they can be cared for at home by their families. It is very important that they are closely monitored.
Dogs will now need plenty of rest and should not overexercise, but if they have the energy, short walks and some playtime are fine.
The diuretic medications will make them more thirsty. Always give unlimited access to drinking water and extra potty breaks.
Salty treats and table foods should be avoided.
There is evidence that supplemental omega-3 fatty acids are helpful for dogs with heart disease. Some prescription diets have this, or your veterinarian can recommend a supplement.

Recovery and Management of Mitral Valve Disease

Mitral valve disease may or may not progress to the extent that it needs to be medically managed. It is important that if a murmur is identified, it is monitored regularly by your veterinarian, with referral to a cardiologist for echocardiograms and additional recommendations if needed.

New dietary research is exploring the benefit of diet in preventing the progression of this disease. Dogs with heart disease need adequate protein in their diets and should not be obese, as this increases stress on the heart. Diets containing omega-3 and medium chain triglycerides, magnesium, and vitamin E are shown to provide much-needed nutrients to overstressed heart muscle.

Mitral valve disease is considered a managed disease, with monitoring and treatment done to prevent the dog’s condition from advancing to the next stage. Mitral valve disease is not considered curable in dogs at this time. The prognosis varies widely, and some dogs will remain in Stage B1 and their lifespan will not be shortened. Other dogs progress steadily into advanced stages. Once a dog has progressed into Stage C (congestive heart failure), the prognosis is guarded.

Featured Image: iStock.com/AzmanJaka