Dr. Dena Fauske, DVM, DACVIM (Cardiology)
Arista | Dallas Owner Veterinarian
Myxomatous Mitral Valve Disease (MMVD)
What is MMVD?
Myxomatous (degenerative) mitral valve disease is a common condition affecting the heart valves of older, small- to medium-breed dogs, although any breed can be affected.
Breeds with increased risk include:
- Cavalier King Charles Spaniel
- Maltese
- Chihuahua
- Yorkshire Terrier
- Miniature Schnauzer
- Dachshund
The underlying cause of the valve degeneration is unknown.
What part of the heart is affected?
The mitral valve sits between the left atrium and left ventricle, which is the main pumping chamber of the heart. Degenerative changes cause the valve to thicken and not close properly, allowing blood to leak backward when the heart contracts. This is called mitral regurgitation, and it means less blood moves forward to the body.
Over time, mitral regurgitation can:
- Cause enlargement of the heart
- Lead to congestive heart failure (CHF)
- While many dogs develop MMVD later in life, only about 25–50% will develop clinical signs of congestive heart failure.
The tricuspid valve (right side of the heart) is also commonly affected, though usually to a lesser degree. Backward flow on that side is called tricuspid regurgitation.
How is MMVD detected and evaluated?
MMVD is most often first identified when a heart murmur is heard during a physical exam. The murmur is caused by turbulent blood flow moving backward through the leaky valve.
Recommended tests may include:
- Thoracic radiographs (chest X-rays) – assess heart size and look for fluid in the lungs
- Echocardiogram (cardiac ultrasound) – evaluates valve function, severity of leakage, and heart enlargement
- NT-proBNP blood test – helps determine the severity of heart disease
These tests help stage the disease and guide treatment decisions.
Stages and Treatment
Stage B1 – Mild disease, no significant heart enlargement
- No medications needed
- Treated as a normal dog at home
- Routine monitoring (annual or semiannual exams)
- Follow-up imaging as recommended (radiographs often sufficient)
Stage B2 – Heart enlargement present, no heart failure yet
- Medications recommended to delay the onset of heart failure:
- Pimobendan (Vetmedin)
- Sometimes an ACE-inhibitor and/or spironolactone
- Periodic monitoring of heart size and clinical signs
- Bloodwork may be recommended to monitor kidney function
Stages C & D – Congestive heart failure present
- Additional medications required:
- Diuretics to remove fluid from the lungs
- Other heart medications as indicated
- Some dogs require brief hospitalization when CHF is first diagnosed
- Close follow-up with blood pressure, bloodwork, and rechecks every 3–6 months
Medications help control clinical signs but do not correct the valve disease.
Advanced Treatment Options
Mitral valve repair surgery is only available at a limited number of specialized centers.
Options include:
- Open-heart mitral valve repair
- Transcatheter edge-to-edge repair (TEER) – a less invasive hybrid technique
These options can be discussed with a veterinary cardiologist if appropriate.
Home Monitoring
Home monitoring is very important for identifying early progression and early congestive heart failure.
Watch for the following signs:
- Increased or labored breathing
- Coughing
- Decreased appetite
- Exercise intolerance
- Weakness or collapse
These signs should prompt a phone call and usually a veterinary visit.
Resting/Sleeping Breathing Rate (RRR)
Monitoring the breathing rate while your dog is asleep or completely relaxed is one of the most sensitive ways to detect early heart failure.
- Normal: less than 30 breaths per minute
- Consistently higher values should prompt a veterinary recheck
Monitoring Recommendations
Stage B1
- Routine exams annually or semi-annually
- Imaging as needed
Stage B2
- Periodic rechecks and imaging
- Bloodwork if on medications
Dogs with CHF
- Rechecks every 3–4 months or after medication changes
- Blood pressure and kidney monitoring
Prognosis
The prognosis for dogs with MMVD varies depending on the stage of disease and the rate of progression.
- Many older dogs with MMVD will not have their lifespan limited by their valve disease
- It often takes years after a murmur is first detected before heart failure develops
- Once congestive heart failure occurs, most dogs can maintain a good quality of life with treatment
- Average survival after the onset of CHF is approximately 12–18 months with consistent therapy
