Mitral Insufficiency-Left Atrial Tear

Mitral Insufficiency is where the mitral valve (on the left side of the heart) valve starts leaking backwards. With a severe leak, the left atrium is usually very enlarged. In some dogs, the left atrium is so large and thin-walled, that it actually tears.

Disease Info

Mitral Insufficiency (MI)- Severe with Left Atrial Tear

(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 where the mitral valve (on the left side of the heart) 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, the left atrium is usually very enlarged
      • This is due to a degeneration of the mitral valve, which separates the left atrium (the receiving chamber) from the left ventricle (the pumping chamber)
    • Left Atrial Tear

      • In some dogs, the left atrium is so large and thin-walled, that it actually tears
        • blood leaks out of the left atrium, and into the heart sac around the heart (the pericardium)
          • pressures within the pericardium become high, and this seals the tear
          • the tear can reoccur
      • These pets virtually always have severe disease
        • Your pet will always have their mitral valve disease (this cannot be reversed)
        • And… your pet can be treated to allow the tear to heal
      • Some of these pets have concurrent congestive heart failure (see Severe Mitral with Congestive Heart Failure)
    • This is an age related degenerative process, and not related to infection or inflammation
  • 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
    • Left atrial tear is uncommon, though we see quite a few cases
    • 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
  • CLINICAL SIGNS (with severe mitral insufficiency with left atrial tear):
    • Signs are readily apparent and sudden in onset
      • Fainting (syncope) is the most common presentation
        • They can be down for a prolonged period of time
        • Some pets will actually have neurologic signs due to sudden loss of blood flow to the brain
      • Fast or troubled breathing
        • Some pets will also have concurrent congestive heart failure
      • Cough is sometimes present
        • Due to fluid in the lungs, or because the heart is compressing the bronchus
  • DIAGNOSTICS (See Tests We Often Perform)
    • Echocardiography (heart ultrasound)
      • We will want to perform echocardiography (heart ultrasound) as soon as possible
        • This is the definitive diagnosis method
        • So we can more accurately stage the degree of leak into the pericardial space
        • Assess for concurrent problems (high blood pressure in the lungs, rupture of a chordae holding the mitral valve in place, decreased heart function)
    • Radiographs (x-rays)
      • We will virtually always want to also have radiographs
      • Radiographs show us how much fluid is in the lungs, how big the heart is, and if there is other lung disease, or collapse of the trachea or bronchi
      • Some pets are in such distress, that we have to put them in oxygen first, and get radiographs when they are a bit more stable
    • Doppler Blood Pressure
      • We will want a blood pressure, because aggressive blood pressure control is essential in these cases
    • Electrocardiogram
      • If there is fainting or heart rhythm abnormalities, we will want to perform an electrocardiogram (ECG or EKG)
    • Labwork will be essential
      • Hearts with disease do not want extra fluid, so we give medications to get rid of excess body fluid
      • Kidneys want fluid
      • We are going to be giving diuretics to get rid of fluid, so monitoring kidney function and electrolytes is essential


  • THERAPY
    • Intervention is required for survival of your pet, and to get back quality of life
      • We can affect the heart in a multitude of ways
      • We will be trying to get less blood to back up, and more to move forward
    • Tapping the heart sac is rarely necessary with this condition
    • 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
    • Oxygen
      • In the short term, in the hospital, if there is significant fluid in the lungs, your pet may have to be in oxygen while the medications start to work
        • With just mitral insufficiency, it is rare to have to do at-home oxygen
    • Diuretics (furosemide, spironolactone, hydrochlorthiazide, torsamide)
      • Decrease the amount of fluids that the heart has to handle and get rid of fluid in the lungs
    • 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
    • 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
    • In the short term
      • These patients are often critical, and short term prognosis can be guarded
        • Really, short term prognosis depends on response to the medications
      • Most pets will respond very well to an aggressive cocktail of medications
        • Sometimes, the amount of fluid in the lungs is so bad that pets will not respond, and have to be humanely euthanized.
    • For the long term
      • If we can control fluid in the lungs in the short term and control blood pressure
      • They can actually survive for quite long periods of time
      • With joint care between a veterinary cardiologist and a family practitioner
        • Your pet lives about 75% longer than without a cardiologist
        • With a multi-medication approach
          • Survival for over a year and 1/2 is achieved in over 50% of dogs
            • These numbers have not been validated for dogs with chordae rupture
  • 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
    •  Monitoring
      • Monitoring at home consists of monitoring eating and activity, and to note breathing and coughing patterns. Because fluid in the lungs causes increased breathing rates as the first sign of congestive heart failure, noting breathing rates is very important. See our Resting Breathing Rates page
    • These cases will need to be monitored, and much more frequently
      • Generally, they will be seen a week after starting treatment
        • 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
      • After that, if all is going well
        • Seeing them every three to four months is typical
          • Typically we monitor radiographs for congestive heart failure, blood pressure, and kidney function
          • If there are odd signs seen clinically or radiographically, then repeat echocardiogram’s are certainly warranted

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
CAUSE: Mitral insufficiency is due to age-related degeneration of the valve
CLINICAL SIGNS: Fainting. Fast or troubled breathing. Cough is often present
POSSIBLE DIAGNOSTICS: Radiographs (x-rays), Echocardiography (heart ultrasound), Doppler Blood Pressure, Electrocardiogram, Labwork
THERAPY: Medical intervention is required for survival of your pet, and to get back quality of life
PROGNOSIS: Short term prognosis is guarded. Long term prognosis can be relatively good if they do well in the short term.
FOLLOW UP CARE: These cases will need to be monitored, and much more frequently