Mitral valve disease in dogs is a very common condition of the heart, typically affecting older dogs. It is a progressive disease that results in the deterioration of the mitral valve, which separates the left atrium from the left ventricle. This can lead to congestive heart failure, which is characterized by a buildup of fluid in the lungs. Mitral valve disease can be treated with medications to help improve cardiac function and attempt to delay the progression of mitral valve disease.

What is the mitral valve and what are its main functions?

The mitral valve is a heart valve located between the left atrium and left ventricle. It has two flaps, or leaflets, that open and close to control the flow of blood through the heart. The main functions of the mitral valve are to prevent blood from flowing back into the atrium and to ensure that blood flows from the atrium to the ventricle in a one-way direction. With normal cardiac physiology, blood enters the left atrium from the lungs, through the mitral valve, and into the left ventricle. From there, blood is pumped to the rest of the body via the aorta.

What is mitral valve disease in dogs?

Mitral valve disease in dogs is characterized by progressive degeneration of the mitral valve, which can lead to mitral valve insufficiency the backflow of blood (regurgitation), and subsequent enlargement of the left atrium and ventricle. The disease progresses over time and the mitral values continue to degenerate, pressure in the left atrium accumulates and this can lead to fluid accumulation in the lungs (pulmonary edema) and congestive heart failure.

Mitral valve disease commonly affects older, smaller breed dogs with an average age of 10. Cavalier King Charles spaniels are predisposed to mitral valve disease at an early age.

What are the causes of mitral valve disease in dogs?

The exact cause of mitral valve disease and degeneration in dogs is unknown but current theories suggest a genetic defect is an underlying cause.

What are the symptoms of mitral valve disease in dogs?

Many dogs with mitral valve disease are asymptomatic with the only clinical sign being a heart murmur that would be heard by your veterinarian. Mitral valve insufficiency and disease will cause turbulent blood flow through the heart that results in a heart murmur. As the disease progresses, clinical symptoms dog owners may notice include:

  • Coughing
  • Exercise intolerance
  • Increased respiratory rate and panting
  • Syncope (collapse)
  • Weight loss

Stages of mitral valve disease in dogs

The American College of Veterinary Internal Medicine (ACVIM) Specialty of Cardiology Consensus Panel has established a staging system for heart disease and failure.

Stage A

This stage starts with dogs that may be at risk for developing heart disease but do not currently have any discernible heart problems (e.g. no audible heart murmur). This stage includes Cavalier King Charles spaniels and other breeds prone to mitral valve disease.

Stage B

This stage includes dogs with structural heart disease but does not show any signs of heart failure. There may or may not be radiological or echocardiographic evidence of heart enlargement.

Stage C

Dogs in this stage have mitral valve disease with clinical signs of heart failure. These dogs will typically respond to traditional therapy for heart failure.

Stage D

Dogs in this stage have end-stage heart failure that often fails to respond to standard therapy for heart disease and failure.

How is mitral valve disease in dogs diagnosed?

Your veterinarian will first perform a physical examination and listen to your dog's heart with a stethoscope. A heart murmur in a specific location is indicative of mitral valve disease. If your veterinarian suspects mitral valve disease, they may order other tests such as:

  • Radiographs (x-rays) - useful for assessing cardiac size and chamber enlargement. X-rays are also valuable in detecting fluid accumulation in the lungs called pulmonary edema
  • Echocardiogram (ultrasound of the heart) - this is a beneficial test as it can directly assess the mitral valve. It can also detect turbulent blood flow through the mitral valve and measure the thickness of the heart.
  • Electrocardiogram (ECG or EKG) - this test may be recommended if your veterinarian detects an arrhythmia when listening to your dog's heart.
  • Blood work (biochemical profile and CBC) - baseline blood work is helpful as it allows your veterinarian to obtain an overall health status for your dog. In addition, 25% of all the blood that leaves the heart (cardiac output) is provided to the kidneys. If there are compromises to heart function, elevated kidney levels may be noticed.

How is mitral valve disease in dogs treated?

The goal of treatment for mitral valve disease is to improve the function of the mitral valve, prevent the progression of the disease, and manage and control the clinical signs of heart failure. Dogs that are in stages A and B often do not require any medical or dietary therapy is required. For those dogs in stages, C and D include treatments that may include:

Angiotensin-converting enzyme inhibitors (ACE inhibitors) - This class of medication works by decreasing the production of angiotensin II, a hormone that can lead to fluid retention and vasoconstriction. A common example is benazepril and it can help the heart and mitral valve by reducing the pressure the heart has to pump against (i.e. reducing afterload).

Pimobendan - This medication is a positive inotrope and increases the strength of contraction of the heart muscle. It also dilates blood vessels and helps to prevent fluid accumulation in the lungs.

Furosemide - This diuretic helps to remove excess fluid from the body by increasing urine output and thereby reducing fluid accumulation in the lungs (pulmonary edema).

Diets that provide a quality source of dietary protein and that have low salt amounts are recommended for dogs with mitral valve disease.

What is the prognosis for mitral valve disease in dogs?

The prognosis for mitral valve disease in dogs greatly depends on the stage of the disease at the time of diagnosis. Dogs in Stage A have a good prognosis, while dogs in Stage D often do not respond to traditional therapy and have a poor prognosis. With aggressive and early treatment, many dogs can live years with mitral valve disease.

Frequently asked questions

How common is mitral valve disease in dogs?

Mitral valve disease is the most common heart disorder in dogs, affecting an estimated 10% of all dogs and making up 75% of all heart diseases in dogs. The disease is more common in older dogs and is rare in dogs younger than 1 year of age, except for Cavalier King Charles dogs.

Is mitral valve disease in dogs treated surgically?

Surgical treatment options are not readily accessible. They're done mostly at university teaching hospitals and select specialty clinics.

What is the life expectancy for dogs with mitral valve disease?

Numerous studies have been performed on dogs with mitral valve disease and life expectancy correlates to the stage of the disease. Depending on the study and classification, median survival rates range anywhere from 2 months for dogs in stage D to over 3 years for dogs with stages A and B.

This article discussed mitral valve disease in dogs. You have learned that mitral valve disease is a condition that affects the mitral valve in a dog's heart and this condition can lead to congestive heart failure. Symptoms of mitral valve disease include difficulty breathing, coughing, and exercise intolerance. Treatment and prognosis are dependent on the stage of mitral valve disease affecting your dog. If you believe your dog may have mitral valve disease, it is important to take them to your veterinarian for a diagnosis.