According to studies, myxomatous mitral valve disease (MMVD) is dogs’ most commonly diagnosed congenital heart disease. MMVD can affect dogs of all ages but is more prevalent in older dogs. It is also more prevalent in some breeds than the others, including Cavalier King Charles Spaniel, Maltese, Cocker Spaniel, and Chihuahua.

What Is Myxomatous Mitral Valve Disease?

Myxomatous mitral valve disease (MMVD, sometimes known as endocarditis) is dogs’ most common heart disease. It’s a degenerative illness that changes both the leaflets and chordae tendineae of the dog’s mitral valve.

A normal mitral valve works as a one-way gate between the left atrium and ventricle of a dog’s heart, allowing blood to pass from the atrium to the ventricle but not vice versa. In MMVD, the mitral valve doesn’t close properly as its leaflets thicken and increase in number as your pet ages.

When there are more leaflets, or they have become too thick, they make your dog’s mitral valve narrow. Meanwhile, damage to the chordae tendineae can weaken or rupture them over time.

Combining these changes means that blood flow becomes less efficient, and it is more difficult for a dog’s heart to push blood forward during each heartbeat. This increases the pressure inside the left ventricle and eventually results in backward leakage of blood into the atrium.


Clinical signs of MMVD are usually gradual in onset, beginning with a slight cough or less commonly gagging. A dog cardiologist will listen to the heartbeat of an animal exhibiting these symptoms to determine if MMVD is present.

  • Heart murmur
  • Coughing
  • Loss of energy and exercise intolerance
  • Swollen abdomen or neck veins
  • Loss of appetite, excessive water consumption, and urination
  • Labored breathing while resting
  • Pacing and restlessness at night, which can disrupt sleep patterns
  • Fainting or loss of consciousness due to low blood pressure caused by heart failure
  • Behavior changes, including being withdrawn, inactive, lethargic, hiding away from family members


Your vet diagnoses the disease using any combination of several tests. Your veterinarian performs a complete physical exam on your dog, including listening to the heart with a stethoscope to identify murmurs and other unusual heart sounds.

  • An electrocardiogram (ECG) test measures electrical activity in the heart muscle, indicating sufficient oxygen to function correctly.
  • Echocardiography is an ultrasound test that can offer more detailed information about how well the valves are working compared to X-rays alone. It also provides additional information on the size of the chambers, the thickness of valve leaflets, and blood flow through them.
  • A dog MRI provides more detailed information than echocardiography and is especially good for looking at the thickness of the heart muscle. You may visit Veterinary Medical and Surgical Group to see how this works.

MMVD Treatment

  • Your vet will prescribe analgesics to ease discomfort. 
  • They may also require blood thinners to prevent blood clots from forming in the heart, lungs, or limbs. 
  • They may also give diuretics or “water pills” to reduce fluid accumulation in the lungs and chest cavity, which can also help alleviate coughing.
  • Digoxin is used to maintain a steady heartbeat, while ACE inhibitors have effectively regulated blood pressure and increased the strength of heart contractions. 
  • Aspirin therapy is prescribed for dogs with severe mitral valve disease that increases inflammation in the heart muscle. However, you should only give it when advised by your veterinarian because aspirin may cause the blood to be a less likely clot, increasing the risk for more severe complications.

Surgical treatment is also available if all other treatments are not effective or have been exhausted. Your vets can surgically repair the mitral valve or replace it, depending on its severity. 

How Long Do Dogs with MMVD Live?

Dogs with mitral valve disease can live with proper treatment and nursing for several years. The quality of life depends on the stage your dog is in. Dogs with MMVD that receive adequate care may survive an average lifespan of 2 to 4 years, while those diagnosed at a later stage tend to live only six months to 1 year.

Remember that all dogs have different situations. Your dog’s life span depends on the severity of their condition and how well they respond to treatment. On top of these, choose a reputable vet hospital or clinic, such as, since they will be your partner in caring for your dog’s well-being.