Mitral Valve Disease (MVD)
MVD is the most common heart disease in dogs. The disease is encountered in all breeds, although it is most common in small and medium sized dogs, from middle to old age.1
Susceptible breeds
Whilst MVD can affect all breeds of dog, including cross-breeds, it is often hereditary and some breeds are at a higher risk of developing MVD, such as the Cavalier King Charles Spaniel, Miniature Poodle, Shih Tzu, Maltese, Miniature Schnauzer, Chihuahua, Cocker Spaniel, Whippet, Dachshund, Pomeranian, Fox Terrier, and Boston Terrier.
Leaky valve
The role of the mitral valve is to make sure that blood flows in the right direction through the left side of the heart. In MVD, the mitral valve becomes thick and lumpy, preventing the valve from closing properly. This means that every time the heart beats, blood leaks through the damaged valve in the wrong direction. This abnormal flow of blood can be heard by a vet when they listen to the heart with a stethoscope and is called a heart murmur.
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The two stages of MVD
There are two distinct stages of MVD:
The first is a long silent stage (typically lasting years), in which a dog with MVD appears healthy and shows no outward symptoms that there is a problem with their heart. This is called the asymptomatic or preclinical stage.
The second is a shorter stage (typically lasting months), in which the heart can no longer cope and the dog shows symptoms of their heart disease. This is called the heart failure stage or congestive heart failure (CHF).
First stage: asymptomatic or preclinical
A dog with asymptomatic MVD will appear outwardly healthy and show no visible symptoms to suggest there is a problem, even though the changes to their heart have already begun. The only warning sign is a heart murmur, which a vet can detect when they listen to the dog’s heart with a stethoscope. A dog with MVD can live for many years without having any symptoms except for a murmur.
However, MVD does slowly progress and get worse over time. As the valve becomes increasingly leaky, the dog’s murmur gets louder and the heart is put under greater strain. To compensate, the heart becomes larger and pumps harder, but eventually the heart can no longer cope with the additional strain and is unable to pump enough blood around the body. This is known as congestive heart failure (CHF).
Second stage: congestive heart failure (CHF)
Symptoms of congestive heart failure can initially be quite subtle. However, as the heart disease progresses, the symptoms become more severe and more noticeable.
Symptoms of congestive heart failure can include:
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Increased breathing rate
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Difficulty breathing
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Tiredness
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Difficulty exercising
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Coughing
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Fainting/collapse
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Weight loss
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Poor appetite
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Swollen abdomen
How is MVD diagnosed by my vet?
When your vet examines your dog, there are a few changes that may suggest your dog has heart disease. The most important is the presence of a heart murmur, which your vet can check for when they listen to your dog’s heart with a stethoscope. If they hear a murmur, they may recommend X-rays or an ultrasound scan to find out if your dog has an enlarged heart.
X-rays
A chest X-ray enables your vet to assess the overall size of your dog’s heart as well as enabling them to check for any fluid in the lungs. Fluid in the lungs isn’t present in the asymptomatic stage of the disease, but it is often present when a dog is in heart failure.
Ultrasound
An ultrasound scan of the heart allows your vet to assess the inside of your dog’s heart. By performing an ultrasound scan, your vet can take measurements of the heart chambers and this helps them to confirm whether the heart is enlarged. You may hear your vet refer to the ultrasound scan as an ‘echo’.
Why do I need to find out if my dog’s heart is enlarged?
Finding out whether your dog has an enlarged heart is very important, as it will allow your vet to:
- Identify whether your dog will benefit from Vetmedin®
- Provide you with an accurate prognosis
- Monitor the progression of your dog’s disease
Both X-ray and ultrasound can be used to determine whether a heart is enlarged; your vet will discuss with you which test(s) will be right for your dog. Neither test is painful but they may require your dog to go into the practice for a few hours or see a heart specialist.
If your dog has an X-ray or an ultrasound scan and their heart is a normal size, it is a good sign. It means that your dog is unlikely to develop heart failure imminently.
However, it’s important to remember that MVD is a disease that gets worse over time. Therefore, even if your dog’s heart is not enlarged, it’s likely that your vet will recommend that these tests are repeated every 6 to 12 months to monitor how their heart disease is progressing.
For more information about MVD, or if you think your dog has a heart murmur, please speak to your vet.
How long until my dog develops congestive heart failure?
Some dogs with an MVD murmur never progress to the stage where they have a large heart and so they don’t develop congestive heart failure. If a dog’s heart does become enlarged due to their MVD, they typically develop congestive heart failure within 2 years.2
How to help your dog
Most importantly, visit your vet to determine whether your dog has an enlarged heart and would benefit from starting on Vetmedin®. There are also changes you can make at home to help your dog:
Diet
Your vet may recommend a change in diet. It’s important that dogs with heart disease aren’t overweight as this can put more strain on their heart, and so your vet may suggest a diet that helps to prevent weight gain or helps with weight loss. Your vet may also discuss a diet for your dog that is low in salt to prevent them from retaining excess water. You shouldn’t make changes to your dog’s diet without consulting your vet first.
Exercise
It is very important to seek your vet’s advice about whether exercise is suitable for your dog and to what level.
Generally, for dogs with asymptomatic MVD, exercise can continue as normal. If your dog has mild symptoms of heart failure, regular light exercise is thought to be beneficial; however, if your dog seems tired, stop exercising and allow them to rest.
Keeping a diary
Try to keep a diary of your dog’s activity level, appetite and demeanour; this will help your vet understand how well they are responding to treatment and how their condition is progressing.
Monitoring breathing rate
Your vet may suggest that you monitor your dog's breathing rate if they have been diagnosed with MVD. Click below for more information on how to do this. Should you have any further questions on whether or not your dog would benefit from monitoring, or how and when to monitor your dog, please contact your vet.
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[1] Keene, BW, et al. ACVIM consensus guidelines for the diagnosis and treatment of myxomatous mitral valve disease in dogs. J Vet Intern Med. 2019; 33: 1127– 1140.
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[2] Boswood A et al. Effect of Pimobendan in Dogs with Preclinical Myxomatous Mitral Valve Disease and Cardiomegaly: The EPIC Study—A Randomized Clinical Trial. J Vet Intern Med. 2016;30:1765-1779.
