Canine Heart Murmur: Learn all there is to know about Mitral Valve Disease

A Complete Guide to a Canine Heart Murmur…

What causes a Heart Murmur? Before we go into detail as to the exact causes we need to take a closer look at the Heart. The Heart is split into two halves with those two halves also split into two separate chambers. A valve also separates these chambers whose main function is to stop blood from flowing back from the ventricle into the atria (the valve does this by closing tightly).

A problem develops when this valve fails as it allows blood to flow backwards which will then produce the classic sound of murmuring (you can hear this sound through a stethoscope). Although a murmur can sometimes be natural there are also secondary causes including birth defects, old age, heart disease and circulatory problems (Bordwell, S. 1994).

Canine Heart Murmur – More Facts…

  • A canine heart murmur is a cardiac disorder that is caused by changes in the heart valves and also changes in their function.
  • Inherited heart disease is classed as congenital and heart disease that develops is called acquired.
  • If the disorder is acquired it may have been acquired through disease, age, anemia and/or high blood pressure.
  • The disorder also relates to an abnormal activity in a dog’s blood flow.

What are the Symptoms of a Canine Heart Murmur?

Symptoms can include…

  • Breathing difficulties.
  • Your dog may develop a blue tongue, mouth and gums.
  • Your dog may appear weak.
  • Sluggish behavior.
  • Your dog may even faint
  • Your dog may struggle with exercise
  • Coughing is another symptom

How is a Heart Murmur Diagnosed?

We advise you to take your dog straight to the vet if you have any concerns about his health, it’s better to be safe than sorry.

A common way to diagnose this problem is for the vet to perform certain tests including an…

  1. Chest X-Rays
  2. Blood tests
  3. Ultrasound on the heart
  4. Echodiagrams
  5. Electrocardiography
  • The treatments, therapy and medications can vary depending on the age of your dog and how serious the problem is.
  • If the heart murmur is benign your vet may encourage a better diet that will counteract any nutrients that maybe lacking in your dogs nutritional plan.
  • If a better diet is advised by your vet, the vet may advise a diet that includes nutrients like Omega-3 fatty acids a low sodium diet, Coenzyme Q10 and Vitamin A also being added to the diet.
  • Your vet may prescribe medications like Enalapril, Lasix or Benazepril to lower your dog’s blood pressure.
  • If the vet has concerns about fluid building up in the organs they may prescribe diuretics.
  • If the problem is very severe, your dog’s vet may need to perform surgical procedures, but this is normally done in older dogs with diseased and damaged heart valves.

There are a variety of heart diseases that can affect your dog including:

  1. Acquired Heart Disease
  2. Chronic valvular heart disease
  3. Dilated cardiomyopathy
  4. Arrhythmogenic right ventricular cardiomyopathy
  5. Myocardial disease
  6. Pericardial disease
  7. Congenital Heart Disease
  8. Patent Ductus Arteriosus (PDA)
  9. Subaortic stenosis
  10. Pulmonic stenosis (PS)
  11. Subvalvular aortic stenosis (SAS)

Dilated Cardiomyopathy: Although Mitral Valve Disease is common in dogs Dilated Cardiomyopathy is more common in larger breeds and Giant Breeds (such as Great Danes). This condition develops when the heart muscle becomes diseased leading to the heart chambers to become enlarged and the walls of the ventricles start to find it more difficult to contract. Dogs that develop Dilated Cardiomyopathy can appear lethargic, cough frequently and may find it difficult to exercise.

The condition is normally diagnosed via a electrocardiogram (where the vet will listen for an abnormal heart rythym i.e. arrhythmia).

Did You Know…?


1. 1 in 3 dogs are diagnosed with a Heart Murmur everyday (that’s equivalent to 3 million dogs)!

2. Did you know that the sound of a normal heart beat is similar to a lub dub, lub dub but in dogs with a murmur the sound changes slightly to a lub-shh-dub or lub-dub-shh.

3. Mitral Valve Disease (MVD) is actually more common in toy and small breeds including the Cavalier King Charles.

Although MVD normally develops in older dogs in the King Charles breed they have the highest onset of the condition – in fact in the early onset of the condition 100% of cases the breed has developed MVD by the age of ten years of age. In fact it is the leading cause of death in the King Charles breed.

4. There are other breeds that are also prone to a Heart Murmur through MVD including Chihauhuas, Lhasa apsos, Cocker Spaniels, Yorkshire Terriers and Miniature Schnauzers.

5. It is possible for affected dogs to live for years with MVD without developing heart failure. However, eventually fluid starts to accumulate in the lungs (congestive heart failure) and the dog’s body is unable to properly function due to a lack of oxygen being circulated.

6. It is possible for medication to prolong a dog’s life there are a variety of factors that can make the problem worst including obesity and environmental factors.

Mitral Valve Disease (MVD)

One of the most common causes of a Heart Murmur in dogs is a condition known as Mitral Valve Disease. The Heart is split into four chambers and also four valves. MVD develops when the connective tissue that helps make up the heart’s mitral valve starts to fail (and degenerate).

When the Mitral Valve starts to fail it is then unable to fully close. This allows blood to seep back into the one of the chambers i.e. the left atrium. This causes the left atrium to become enlarged. Mitral Valve Disease is diagnosed by the vet listening to the sound of the leakage which is called a Murmur.


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