Degenerative mitral valve disease is an acquired disease, responsible for 75% of all canine heart disease. It affects up to seven million dogs in the United States alone.


Degenerative mitral valve disease affects the mitral valve, a flap that is located on the left side of the heart, between the atrium and the ventricle.  This valve, whose tissue tends to degenerate with age, gradually thickens and, losing its elasticity, is no longer impervious.  This lack of closure leads to abnormal blood flow inside the heart, known as mitral regurgitation.

As the disease worsens, the chordea tendineae (cords) connecting the valve to the left ventricle may rupture.  This complication can lead to pulmonary edema (a buildup of fluid in the lungs making it difficult to breathe) and other complications that are detrimental to the dog’s life.  

Degenerative mitral valve disease may appear from 5 years of age in more than 80% of small dogs under 15kg.  In the Cavalier King Charles and the Dachshund, it is a very common genetic disease that can appear from the age of 1 year.  It is also commonly observed that males are more frequently and more severely affected than females.

The disease is progressive, gradually worsening over time, more or less rapidly depending on the individual.  The tricuspid valve is also affected in ⅓ of cases.  Medical treatment to relieve the work of the heart and cure pulmonary edema should be prescribed as early as possible in order to prolong the dog’s life to the maximum.  This treatment is updated once or twice a year on a case-by-case basis through clinical, blood, and ultrasound checks by a veterinarian.  

At the onset of the disease, the heart performs a physiological adaption work called the compensatory phase, the disease is at this stage “dormant”.  When the adaptive capacities of the heart are exceeded, symptoms such as fatigue, cough, and fainting may develop.  When these symptoms are present, the disease is in its “decompensated phase”. Medicines are essential and prescribed for life, unless surgery is decided at the most appropriate time in the dog’s life.

Large dogs also suffer from Mitral Valve Disease, although it is less common, and are typically less ill than small dogs. Some medium and large breeds are predisposed to heart disease, but not by an anomaly of the valve, but to cardiac muscle disease known as cardiomyopathy.  This accounts for 15-20% of medium and large breed’s heart disease.   

Photo courtesy of The Pet Authority

Detection and Palliative Care

Typically, the first sign of mitral degeneration is detected as a low grade heart murmur that increases over time based on many factors including heart muscle strength, age, chord rupture, or other complicating factors. Radiological examinations, echocardiograms, doppler ultrasounds, electrocardiographic, and blood tests (NT -proBNP and Troponin I) will allow a complete cardiac assessment to be carried out in order to classify the insufficiency in the heart.  According to the American College of Veterinary Internal Medicine (ACVIM):

  • ACVIM Stage A: Dogs with no murmur or symptoms but who are at risk of developing valvular heart disease according to their breed. These include Cavalier King Charles spaniels and other small breeds of dogs.

  • ACVIM Stage B1: Dogs with heart murmurs but no heart enlargement or symptoms.  No treatment is required at this time.

  • ACVIM Stage B2: Dogs with heart murmurs, enlarged left atrium and ventricle.  Treatment is required to slow the development of congestive heart failure which may include an (ACE) inhibitor or pimobendan according to a recent study (EPIC trial), which works by relaxing the blood vessels, which helps to lower blood pressure.

  • ACVIM Stage C: Dogs with heart murmurs, heart enlargement, and symptoms of congestive heart failure.  Treatment may be increased to include an inodilator such as pimobendan, and more importantly, furosimide, a diuretic to help keep fluid from collecting in the lung tissue.

  • ACVIM Stage D: Dogs not responding to the standard treatment for congestive heart failure may require permanent oxygen therapy and hospitalization at the end of life along with advanced medications.

This disease requires a lifetime of medical follow-up with an update of the medical treatment modeled on the course of the diseases progression, determined on a case-by-case basis.  Heart failure dogs suffer from fatigue, coughing, fainting, labored breathing, anorexia, and eventual death from refractory pulmonary edema and/or cardiac arrest.