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Mitral Valve Disease in Dogs

What Is Mitral Valve Disease in Dogs?

Mitral valve disease in dogs affects the functionality of the heart’s mitral valve, a crucial regulator of blood flow between the left atrium and ventricle. To comprehend this condition, it’s helpful to envision the heart as a pump that propels freshly oxygenated blood from the lungs throughout the body. When the mitral valve functions properly, it prevents any reverse flow of blood from the ventricle to the atrium during heart muscle contractions.

However, in cases of mitral valve disease, the valve’s efficiency diminishes, leading to potential leakage of blood in the wrong direction during muscle contractions. While a small amount of backflow may initially pose no significant problem, over time, the valve may thicken and stiffen, exacerbating the volume of blood flowing back. Consequently, the heart’s pumping efficiency decreases, prompting the heart muscle to compensate by thickening, which enlarges the overall size of the heart.

In advanced stages, mitral valve disease may cause fluid accumulation in the lungs due to the heart’s inability to keep pace, resulting in pulmonary edema. This accumulation of fluid in the lungs is indicative of congestive heart failure in dogs.

Mitral valve disease in dogs is also referred to by other names such as degenerative mitral valve disease or canine myxomatous mitral valve disease.


During the early stages of mitral valve disease, there might not be any noticeable symptoms. However, as the condition progresses, you may observe the following signs:

  • Exercise intolerance, where the dog tires easily or after minimal effort
  • Coughing
  • Rapid breathing
  • Increased effort in breathing
  • Clear nasal discharge
  • Restlessness, difficulty resting comfortably and constantly moving around
  • Decreased appetite


Mitral valve disease is a prevalent condition among dogs, particularly observed in smaller breeds as they grow older. Studies indicate that around 85% of small-breed dogs develop mitral valve disease by the age of 13.

There’s evidence suggesting a genetic predisposition to mitral valve disease, as it is commonly observed in breeds such as Cavalier King Charles Spaniels, Dachshunds, and certain terrier breeds.


Veterinarians employ various methods to diagnose valve disease in dogs:

  • Physical examinations involve evaluating the heart for murmurs, which are early indicators of mitral valve disease. Murmurs are detected and graded by listening to the dog’s chest using a stethoscope.
  • Reviewing the medical history helps veterinarians note any recent changes in breathing, coughing, or behavioral differences that could signify advancing mitral valve disease.
  • Radiographs (X-rays of the chest) are conducted to assess heart size, shape, and any signs of fluid accumulation in the lungs.
  • NT ProBNP testing is performed on blood samples to detect strain on the heart muscle. Elevated levels indicate the presence of mitral valve disease and its severity in causing changes to the heart muscle.
  • Echocardiograms (ultrasounds of the heart), typically conducted by veterinary cardiologists, provide detailed images of the heart muscle and valves, measure heart function, and are considered the most effective method to diagnose mitral valve disease.
  • ECGs (electrocardiograms) are used to detect arrhythmias, which indicate abnormal electrical activity in the heart.
  • Blood pressure measurements are taken to assess for high blood pressure, which can be associated with heart disease.
  • Complete blood counts, chemistry panels, and urinalysis are laboratory tests conducted to monitor overall health, organ function, and kidney values, especially crucial if dogs are under medication or if there are concerns regarding blood pressure.

Mitral Valve Disease Stages

Veterinary cardiologists have devised a classification system to categorize the severity and progression of the disease:

  • Stage A: Dogs in this stage show no signs of the disease yet but are at a high risk of developing it, especially considering breed-specific factors.
  • Stage B1: Dogs in this stage exhibit minimal blood leakage between the atrium and ventricle, along with mild enlargement of the heart muscle.
  • Stage B2: This stage indicates increased blood leakage and significant enlargement of the heart. Medications are typically prescribed at this point.
  • Stage C: Dogs in this stage experience congestive heart failure and necessitate medication for treatment. Standard medication doses are administered, and depending on severity, hospitalization with supplemental oxygen may be required for initial treatment.
  • Stage D: Dogs in this advanced stage have congestive heart failure and do not respond to standard medication doses. Aggressive medication dosages are attempted, but often with limited response. Dogs in Stage D require hospitalization for oxygen support and intravenous medications in an attempt to improve their condition.


The treatment approach for mitral valve disease in dogs varies depending on the stage of disease progression: For dogs in Stages A or B1, monitoring is typically sufficient, and medication is usually not required. However, for Stages B2, C, and D, medication becomes necessary.

Supportive Care:

  • Dogs experiencing acute congestive heart failure often require hospitalization with supplemental oxygen and injectable medication to stabilize their condition.
  • Once stable on oral medication, dogs can be cared for at home by their families. Close monitoring is essential.
  • Dogs should get plenty of rest and avoid overexertion, although short walks and moderate playtime are acceptable if they have the energy.
  • Diuretic medications may increase thirst, so ensure unlimited access to drinking water and provide extra potty breaks.
  • Avoid salty treats and table foods.
  • Evidence suggests that supplemental omega-3 fatty acids are beneficial for dogs with heart disease. Some prescription diets contain omega-3 fatty acids, or your veterinarian can recommend a suitable supplement.

Living and Management

Mitral valve disease may or may not advance to the point where medical intervention is necessary. It’s crucial that if a murmur is detected, regular monitoring by a veterinarian is initiated, with potential referral to a cardiologist for echocardiograms and additional guidance if required.

Recent dietary studies are investigating the potential benefits of nutrition in halting the progression of this disease. Dogs with heart disease require adequate protein intake and should maintain a healthy weight, as obesity exacerbates stress on the heart. Diets enriched with omega-3 fatty acids, medium chain triglycerides, magnesium, and vitamin E are known to offer essential nutrients to overburdened heart muscles.

Mitral valve disease is deemed a managed condition, necessitating monitoring and treatment to hinder the dog’s condition from advancing to the next stage. Presently, mitral valve disease is not curable in dogs. Prognosis varies significantly, with some dogs remaining in Stage B1 without a shortened lifespan, while others steadily progress to advanced stages. Once a dog enters Stage C (congestive heart failure), the prognosis becomes guarded.

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