Mitral Insufficiency: A Leading Cause of Heart Failure in Cats

When your veterinarian listens closely to your cat’s chest, he’s listening for three major things:

  • Respiratory sounds
  • Heart rhythms
  • Heart valve sounds

There are four valves in the heart that ordinarily and normally produce the characteristic “lub dub,” produced by the heart valve opening and closing. When a valve doesn’t open or close properly the result is turbulence that produces a “whoosh” sound. Listening carefully allows the murmur to be localized. While any valve can be involved, the most commonly involved valve is the valve between the left atrium and the left ventricle – the “mitral” valve.

While mitral valve disease can be from a stricture (abnormal narrowing), most commonly it is associated with a leaky valve or “valvular insufficiency.”

Causes of mitral insufficiency

Most mitral valve insufficiency is due to distortion of the free edge. Most often this is associated with deposits of tissue. Normally, when the heart beats, the ventricles pump the blood out to the arteries. When the valves are unable to create a seal, the pumping effort is less efficient and some of the blood is pumped back up stream into the left atrium. This process is progressive as the valve becomes more abnormal and the result is impaired circulation. To help the circulation keep up, the body retains fluid that ultimately accumulates in the lungs and can lead to congestive heart failure.

What are the signs of mitral insufficiency?

Early in the course of the disease there are no signs except for the presence of the murmur that the veterinarian hears on examination. Murmurs are graded from 1-5 based on the intensity of the murmur and the ability to feel the murmur (referred to as a “thrill”). Surprisingly the severity of clinical signs may have little correlation with the intensity of the murmur. Ultimately, the heart decompensates and loses its ability to move blood as needed. The results are:

  • Shortness of breath
  • Exercise intolerance
  • Coughing and severe distress (due to fluid buildup in the lungs)

Diagnosing mitral insufficiency

Diagnostics of mitral insufficiency may require an Electrocardiogram and/or an Echocardiogram to evaluate the strength of the ear and size of the chambers.

Other tests include a blood count to evaluate the function of other organs such as the kidneys and liver. Not all cats with mitral insufficiency have congestive heart failure, and in fact not all cats that have a murmur and cough have progressed to heart failure.

There is a relatively new blood test to evaluate whether a cat has a heart murmur. Referred to as NT-proBNP it is a screening test to differentiate between normal and reduced left ventricular function. This analysis is an excellent prognostic tool in early onset heart failure. This analysis is available commercially and should be considered in affected cats to determine a clinical approach and course.

Treatment of mitral insufficiency

Treatment of valvular disease in humans often involves the surgical repair or replacement of the affected valve. Success rates of these treatment options are not as high in people as they are in cats; however, In cats such procedures are limited in application and availability. The cost of the procedure is between $10,000 and $12,000 which is unfortunately currently beyond the reach of most cat guardians.

Treatment of congestive heart failure

According to veterinary cardiologists at Tufts University Cummings School of Veterinary Medicine, the primary goals of treating congestive heart failure (caused by mitral insufficiency) are to reduce the buildup of fluid and to increase the amount of blood being pumped by the heart to the lungs and the rest of the body. Medical management of congestive heart failure involves a variety of drugs working in concert to enhance cardiac function.

Prognosis of mitral insufficiency and congestive heart failure

The prognosis of mitral insufficiency with congestive heart failure is unpredictable and at very best guarded. It depends on the severity of the causative condition and response to medical management. However, with appropriate management and lifestyle changes like exercise restriction and weight control as well as sodium intake reduction, affected cats can live an average of 9-10 months.

If you have any questions or concerns, you should always visit or call your veterinarian -- they are your best resource to ensure the health and well-being of your pets.


This report, issued by the ACVIM Specialty of Cardiology consensus panel, revises guidelines for the diagnosis and treatment of myxomatous mitral valve disease (MMVD, also known as endocardiosis and degenerative or chronic valvular heart disease) in dogs, originally published in 2009. Updates were made to diagnostic, as well as medical, surgical, and dietary treatment recommendations. The strength of these recommendations was based on both the quantity and quality of available evidence supporting diagnostic and therapeutic decisions. Management of MMVD before the onset of clinical signs of heart failure has changed substantially compared with the 2009 guidelines, and new strategies to diagnose and treat advanced heart failure and pulmonary hypertension are reviewed.


Mitral Valve Disease in Dogs

One of the most common causes of a heart murmur in dogs is a disease called Canine myxomatous or degenerative mitral valve disease (MMVD). It primarily affects older, small to medium size dogs, however, any dog can be affected.

What is Myxomatous Mitral Valve Degeneration (MMVD)?

Let’s learn some basic anatomy and physiology to understand what causes a heart murmur in dogs. The heart is responsible for pumping blood around the body. The blood only travels in one direction through the heart. The heart has four ‘chambers’ called the right atrium, right ventricle, left atrium, and left ventricle.

To enter each chamber there is a ‘one-way door’ (valve). The mitral valve is the valve between the left atrium and the left ventricle.

In MMVD, the mitral valves are thickened and too short. This means that the one-way door fails to form a complete seal, allowing blood to leak back into the left atrium. This abnormal flow of blood causes the turbulence we hear like a heart murmur in dogs.

Over time, MMVD may lead to congestive heart failure (CHF). This happens when the heart becomes too weak to push the blood in the correct direction, leading to excess fluid accumulating in the lungs.

What causes mitral valve disease?

The causes of mitral valve disease are unclear. However, there are a number of implicated genetic factors that make mitral valve disease a heritable cardiac disease. What essentially happens is the degeneration of the mitral valve, which compromises its ability to work like a one-way door.

Dogs at high risk for developing MMVD include the following. However, any small to medium-sized breed dog can develop MMVD:

  • Cavalier King Charles Spaniel
  • Cocker Spaniel
  • Chihuahua
  • Miniature Schnauzer
  • Maltese

How is myxomatous mitral valve degeneration (MMVD) diagnosed?

If your vet detects a heart murmur on a physical exam, you will be recommended tests to diagnose what is causing the abnormal sound in the heart.

An echocardiogram is recommended. This is an ultrasound of the heart performed by a specialist. An echocardiogram is extremely valuable because it will diagnose the cause of the heart murmur. It will also examine the health of the heart valves, measure the blood pressure to the lungs, and examine secondary changes to the heart, including abnormal thickness.

This is an echogram being performed on a patient.

A chest X-ray may also be recommended because it helps us examine the lungs for any fluid and the size of the heart. Sometimes, if the heart gets too big, it can put a lot of pressure on the windpipe.

This is a chest x-ray of a patient. The arrows that you can see on the x-rays are measuring the patient’s Vertical Heart Score.

What are the signs of a heart murmur?

A heart murmur on its own is often accompanied by NO signs. That’s why every year your veterinarian will check your dog’s heart for any murmurs. If the heart murmur is detected too late, there may be evidence of heart disease instead.

What are the signs of heart failure?

A heart murmur can progress into congestive heart failure. This is a serious condition where their lungs get congested with fluid. You may notice your fur-baby has a cough, exercise intolerance, or difficulty breathing.

  • Lethargy
  • Fainting
  • Collapsing
  • Coughing
  • Gagging
  • Trouble breathing
  • Exercise intolerance
  • Reduced appetite
  • Swelling in the abdomen
  • Muscle loss

Coughing can be caused by heart disease for a couple of reasons. First of all, the heart getting bigger can push on the windpipe in the chest causing coughing. Secondly, if the leaky mitral valve is letting too much blood flows backward, fluid accumulates in the lungs, causing coughing.

That said, not all coughing means heart disease. In other cases, coughing may be caused by a respiratory issue rather than a heart issue. This includes bronchitis, allergies, pneumonia, asthma, or kennel cough.

What do I do now that my dog has a heart murmur?

According to the American College of Veterinary Internal Medicine (ACVIM), an echocardiogram needs to be performed every 6 months. This specialist panel of cardiologists stresses the importance of monitoring the disease very closely because it’s easier to prevent heart disease than play catch-up with congestive heart failure (CHF).

A heart check-up with your veterinarian is also recommended every 6 months once a heart murmur is detected.

Why is it so important to repeat the echocardiogram and/or chest x-rays?

There are different stages of heart disease:

  1. Stage A – Dogs at high risk of developing heart disease. No disease is present yet.
  2. Stage B1 – A murmur is heard but there are no visible signs of heart failure or heart enlargement.
  3. Stage B2 – A murmur is heard but there are no visible signs of heart failure. There is evidence of heart enlargement. Heart medication needs to be started at this stage. However during this stage, owners do not think their pet is deteriorating because they are still not showing any signs (e.g., coughing, lethargy, inappetence). The only way to tell if your dog needs to start medication is a heart echocardiogram every 6 months.
  4. Stage C – Heart disease is worsening and signs of heart failure are apparent (eg. coughing, lethargy, fainting). More medication is usually required at this stage.
  5. Stage D – End-stage heart disease which is not responding to treatment. Signs of heart failure.

How can do you treat Mitral Valve disease?

There are different treatment plans depending on what stage heart disease your dog has.

  • Stage A and B1 do not require any heart medication.
  • Stage B2 requires daily heart medication tablets to slow down the progression of congestive heart failure.
  • As heart disease progresses, multiple medications daily may be required to help control heart failure.

What is the prognosis of Myxomatous Mitral Valve Degeneration?

The prognosis of newly diagnosed MMVD varies considerably. A heart murmur can be big news for a paw-parent. But the earlier the diagnosis is made, the better the prognosis for your dog. It is very important to investigate, stage and treat a heart murmur properly because heart murmurs can lead to rapid deterioration.

At My Vet Animal Hospital, we work closely with Specialists in Small Animal Medicine and advanced training in Cardiology. We are able to organise a specialist to come to our clinic for an echocardiogram, rather than travelling to a specialist hospital. We also offer diagnostic x-rays and blood testing in house for immediate results. If your dog needs special heart medication and doesn’t like tablets, we can also offer personalised compounded medicine with added flavour including chicken, beef or fish. This is our way to ensure your dog has an accurate course of diagnosis, access to gold-standard monitoring tests and the best treatment.


Myocarditis is a focal or diffuse inflammation of the myocardium with myocyte degeneration and/or necrosis. Myocarditis is rare in companion animals, although there are numerous causes, including several viruses and bacteria. Canine parvovirus (see Canine Parvovirus), encephalomyocarditis virus (see Encephalomyocarditis Virus Infection), and equine infectious anemia virus (see Equine Infectious Anemia) can cause myocarditis. Myocardial degeneration is seen in lambs, calves, and foals with white muscle disease and in pigs with mulberry heart disease or hepatosis dietetica. Streptococcus spp are the most common cause of bacterial myocarditis in horses. Salmonella, Clostridium, equine influenza, Borrelia burgdorferi, and strongylosis are other recognized causes. Mineral deficiencies (eg, iron, selenium , copper) can also result in myocardial degeneration (not myocarditis). Deficiencies of vitamin E or selenium may cause myocardial necrosis. Cardiac toxins include ionophore antibiotics such as monensin and salinomycin, cantharidin (blister beetle toxicosis, see Cantharidin Poisoning), Cryptostegia grandiflora (rubber vine), and Eupatorium rugosum (white snakeroot). These diseases cause typical signs of CHF. In horses, signs of right heart failure are common and include ventral edema, ascites, venous congestion, and jugular pulsations. A heart murmur of mitral or tricuspid regurgitation is usually audible as well as an irregular rhythm. Atrial fibrillation is common, and ventricular or atrial premature complexes may also be seen. Echocardiography reveals chamber dilation and poor contraction with essentially normal valves. Neutrophilic leukocytosis and hyperfibrinogenemia are common. Cardiac isoenzymes (CK, troponin, and lactate dehydrogenase) are often increased.

Treatment should be aimed at improving cardiac contractility, relieving congestion, and reducing vasoconstriction. Pimobendan and digoxin are used most commonly to improve contractility. Furosemide is indicated to control signs of pulmonary edema. Corticosteroids are often used when cardiac isoenzymes are increased and a viral infection is deemed unlikely.

Chagas’ Myocarditis:

Trypanosoma cruzi, a flagellate protozoa, causes Chagas’ disease (see Chagas’ Disease). Acutely, ECG abnormalities such as first-, second-, or third-degree AV block right bundle-branch block sinus tachycardia and depressed R wave amplitude are noted. There are usually no echocardiographic abnormalities during the acute phase however, sudden death is a concern. An asymptomatic latent phase then develops for 27–120 days in dogs, followed by a chronic stage demonstrating systolic dysfunction indistinguishable from DCM. Treatment for the chronic phase is as for DCM but is typically ineffective at controlling signs of progressive myocardial failure. The disease is most commonly identified in southern states (eg, Texas) but may be spreading.

Tickborne Myocarditis:

Lyme disease (see Lyme Borreliosis) is caused by the spirochete Borrelia burgdorferi infection might result in myocardial disease. In people, it causes a usually reversible third-degree AV block. Animals developing myocardial disease secondary to Lyme infection may, at least in theory, have ECG abnormalities such as ventricular arrhythmias or conduction disturbances such as first-, second-, or transient third-degree AV block. However, a recent study failed to identify evidence of any tickborne organism in a group of dogs presented for third-degree AV block. Two dogs with severe ventricular tachyarrhythmias with a high antibody titer to Anaplasma phagocytophilum required prednisone and azathioprine to control the arrhythmias. There are no reports of DCM due to these organisms in dogs or cats.

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