Mitral Insufficiency-Myocardial Dysfunction

Mitral Insufficiency is where the mitral valve (on the left side of the heart) valve starts leaking backwards. Myocardial dysfunction is where the heart muscle does not function appropriately.

Disease Info

Mitral Insufficiency (MI)- with Myocardial Dysfunction

(also called mitral regurgitation (MR), chronic degenerative valve disease (CVD), myxomatous degeneration or endocardiosis )

Mitral Insufficiency or Mitral Regurgitation


  • DEFINITION (What it is):
    • Mitral insufficiency is due to a degeneration of the mitral valve, which separates the left atrium (the receiving chamber) from the left ventricle (the pumping chamber)
      • The valve starts leaking backwards, so that blood flows both forward and backward within the heart.
        • There are varying amounts of leak
          • This usually (but not always) corresponds to how enlarged the chambers get
      • With a severe leak backwards through the valve, chamber enlargements are quite significant
    • This is an age related degenerative process, and not related to infection or inflammation
    • Myocardial dysfunction is where the heart muscle does not function properly
  • EPIDEMIOLOGY (Who gets it):
    • Mitral insufficiency is a disease of small breed dogs, though we see occasional cases in medium and large breed dogs
      • It is very common, seen in about 75% of all canine heart cases
        • about 30% of cases will have degeneration of both the mitral and tricuspid valves
        • about 10% of cases will have only tricuspid valve degeneration (see Tricuspid Insufficiency)
      • These breeds include miniature Poodles, minature Schnauzers, terriers, Dachsunds and American Cocker Spaniels.
        • Cavalier King Charles Spaniels
          • are at increased risk for developing the disease
          • occurs earlier in this breed
      • It occurs in older pets
        • > 5 years
    • Myocardial dysfunction more commonly is seen in medium or large breed dogs
    • It is very rare in cats


  • CAUSE:
    • Mitral insufficiency is due to age-related degeneration of the valve
      • It appears to be related to collagen disorganization at the cellular level
      • It is not related to
        • infection
        • inflammation
        • dental disease (though dental health is important for your pet)
      • There is probably a genetic component since we see this commonly in certain breeds, but these genes have not been identified
    • Myocardial dysfunction is often present in humans, and so large breed dogs more resemble the human form of the disease. It is actually more remarkable that small breed dogs retain relatively good function.
  • CLINICAL SIGNS (with severe mitral insufficiency and myocardial dysfunction):
    • Signs are readily apparent
      • Exercise intolerance
      • Weakness
      • Fainting
      • Cough is often present
        • Due to the enlarging heart pressing up on the bronchus (lower airway)
      • Fast breathing if congestive heart failure is present (see the congestive heart failure page)
  • DIAGNOSTICS (See Tests We Often Perform)

    • Echocardiography (heart ultrasound)
      • Staging of the mitral valve disease is typically performed with echocardiography (heart ultrasound) and this is the only way to document decreased heart function
    • Doppler Blood Pressure
      • We will want a blood pressure to make sure blood pressure is not too high and causing progression of disease
    • Radiographs (x-rays)
      • If cough is present, radiographs (x-rays) will be recommended
    • Electrocardiogram
      • If there is fainting or heart rhythm abnormalities, we will want to perform an electrocardiogram (ECG or EKG)


  • THERAPY
    • Therapy at this stage will no doubt be started
    • Inodilators (pimobendan)
      • Make the heart pump blood forward more effectively
        • Use of this medication before the onset of signs with this severity of disease has been shown to not only delay the onset to congestive heart failure, but also increase survival once a pet has gone into congestive heart failure
    • Vasodilators (amlodipine, benazepril, enalapril, hydralazine, others)
      • decrease blood pressure and make it easier for the heart to pump effectively
        • Allowing more blood to be pumped forward, and less to back up will be part of what we will do to decrease signs and improve survival
    • Hormone system control (benazepril, enalapril, spironolactone)
      • In heart disease, circulating hormones get activated that make the disease progress
        • Decreasing these circulating hormones can improve survival
    • Rhythm disturbance control (Digoxin, Diltiazem, Mexilitine, Sotalol, others)
      • This is pretty uncommon in mitral insufficiency, but we do see it
    • Diet
      •  See our Food and Diets Information page
        • A severely restricted salt diet such as “Heart diet or H/D” is often not eaten well at all by animals
        • It is more important that your pet eat and eat well, than to stick to the salt restricted diet, even if they won’t eat it.
          • The medications are powerful, and will usually work even if your pet is on regular food.
        • Do not give high salt items such as pork, lunch meats, salted popcorn or high-salt treats.
    • Exercise
      • Exercise is usually moderately restricted
        • They can exercise normally if they want to
        • Restrict the amount or length of exercise
          • Restrict long ball or frisbee throwing, swimming
          • Climbing 14er’s may not be tolerated, and walking in the flats is often better
  • PROGNOSIS
    • For the short term, excellent
    • These pets will progress onward to significant disease, and we want to delay this as much as possible.
      • With good care, it is possible for these pets to live for years at this stage
        • Some will decompensate much sooner than we would like, however
      • We also want to make sure you see signs of progression quickly so we can address it quickly
  • FOLLOW UP CARE
    • We understand that your money has to be spent wisely to be able to monitor and treat your pet for it’s lifetime, so we are very respectful of your finances and yet provide excellent care for your pet
      • We work as a team with your family veterinarian, and maintaining routine and non-specialist care is a very important part of our consideration
    • These cases will need to be monitored, and more frequently
      • How and how often they should be monitored will vary by the cardiologist or practitioner, and also depends on both the pet and the client
        • At this stage, with just severe mitral insufficiency and no right heart involvement, switching to radiographs (x-rays) for routine monitoring is both clinically appropriate and more cost effective for the client
          • With radiographs, congestive heart failure (fluid in the lungs) can be assessed, which cannot be assessed by echocardiography
        • If there are odd signs seen clinically or radiographically, then repeat echocardiogram’s are certainly warranted
        • Monitoring and controlling blood pressure is very helpful at this stage
        • Monitoring renal function, especially on some of the heart drugs, will be important

Quick Info

DEFINITION (What it is): Mitral insufficiency is due to a degeneration of the mitral valve, which separates the left atrium (the receiving chamber) from the left ventricle (the pumping chamber)
EPIDEMIOLOGY (Who gets it): Mitral insufficiency is a disease of small breed dogs. Myocardial dysfunction often occurs in larger breed dogs.
CAUSE: Mitral insufficiency is due to age-related degeneration of the valve
CLINICAL SIGNS: These pets may show signs of "slowing down", and are often attributed to age. Cough can be present due to the enlarging heart pressing up on the bronchus (lower airway)
POSSIBLE DIAGNOSTICS: Echocardiography (heart ultrasound) Radiographs (x-rays) Electrocardiogram Doppler Blood Pressure Holter Monitor
THERAPY: Therapy is medical in nature
PROGNOSIS: Depending on the severity of the disease process
FOLLOW UP CARE: The testing performed often is case dependent