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Heart disease in small to medium dogs

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Mitral Valve Disease (MVD)

Mitral Valve Disease (MVD) is the most common form of heart disease that develops in dogs. It generally occurs in small to medium size dogs rather than big dogs.  

There seems to be a genetic tendency to the development of MVD in certain breeds, which include: Cavalier King Charles Spaniels, Poodles, Schnauzers, Chihuahuas, Fox Terriers and Boston Terriers. 

Male dogs are more commonly affected than females and it is mostly older dogs who tend to show signs of this disease, although young dogs can be affected too. MVD is a disease affecting the surface of the heart valves. Other terms you may hear used to describe MVD are endocardiosis or valvular insufficiency. 

In MVD, one of the heart valves gradually becomes thickened, lumpy, distorted and leaky, so that when the ventricle pumps, some of the blood flows backwards into the atrium. This backward flow creates a noise that your vet can hear with a stethoscope, and is called a murmur. Vets often grade a murmur depending on how loud they are compared to the normal sounds when the heart beats. 

This leaking means that the heart is working less efficiently and as MVD progresses your dog will start becoming unwell and will show signs of heart failure.


How do I recognise MVD in my dog?


Signs of heart failure can initially be quite mild and so may be difficult to pick up. However, as the disease progresses, the signs can become more severe as the heart cannot compensate anymore. This stage is known as congestive heart 
failure, when the heart is no longer able to pump sufficient blood around the body. 

Fluid then builds up and the vital organs won’t be supplied with as much blood and oxygen as they require causing the following clinical signs: 

Signs include: 

  • Reduced ability to exercise 
  • Coughing 
  • Difficulty in breathing or a change to breathing rate 
  • Fainting 
  • Lack of energy or depressed appearance 
  • Poor appetite 
  • Weakness 
  • Anxiety and restlessness during the night

How is MVD diagnosed by my Vet?

Regular veterinary visits are very important for early detection of heart disease and to monitor the treatment of a dog once heart disease has been diagnosed. When your vet checks over your dog, they may find signs relating to heart disease or even congestive heart failure. Listening to your dog’s heart with a stethoscope will allow your vet to pick up a murmur if it is present. The heart rate and rhythm can also be assessed using a stethoscope. Your vet may also detect harsh sounds when listening to the lungs. The examination may also pick up other signs indicating that your dog’s heart is not working well such as fluid in the abdomen and poor pulses. Often, further tests are needed to help determine the degree of your dog’s problem. These may include:  

  • Blood tests:
    Blood tests may be recommended to check your dog’s overall health to see if they are suitable for medication and to check that the rest of their body is healthy.  There are also some specific heart blood tests.

  • X-rays:
    X-rays are very useful to assess your dog’s heart and lungs. Commonly when a heart is having problems it will get larger and fluid may build up
    on the lungs. Both of these can be detected with X-rays.  
  • Echo(cardiogram):
    This is an ultrasound scan of the heart and can be used to assess the heart whilst in action. The heart’s walls, chambers, valves and blood vessels can be accurately observed. Whilst ultrasound is the most accurate method of diagnosing heart disease, it may not be necessary in some of the more straightforward heart disease cases.

  • Electrocardiogram:
    Electrocardiograms (ECGs) can record the electrical activity of the heart and can be used to diagnose rhythm problems. 

How to help my dog


Your vet may recommend a change in diet. It is beneficial for dogs with heart disease not to be overweight as this can put more strain on their heart. Your vet may suggest a diet that could help to prevent weight gain or help with weight loss. They may also discuss a diet for your dog that is low in salt to prevent them from retaining excess water. You should not make changes to your dog’s diet without consulting your vet first – if you are at all concerned, please check with a member of the Companion Care team for advice.


Your vet may suggest that you monitor certain aspects of your dog’s health to help gain a better understanding of how their heart is coping. There are two main ways in which you can monitor your dog’s heart condition at home:   

  1. Monitor your dog’s sleeping breathing rate 
  2. Keep a diary of their activity levels, appetite and demeanour 

Both of these methods of monitoring your dog’s health may help your vet understand how their condition is progressing. Should you have any further questions on monitoring your dog with heart disease, then you should speak to a member of the Companion Care team.