Small Dogs

Mitral Valve Disease (MVD)

Mitral valve disease (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 age (4-5 years+). MVD affects all breeds of dogs including cross-breeds, however some breeds such as the Cavalier King Charles Spaniel, Miniature Poodle, Miniature Schnauzer, Chihuahua, Fox Terrier, and Boston Terrier are even more likely to develop the disease.

In MVD, the mitral valve in the heart becomes thick, lumpy, distorted and leaky. With each heartbeat, blood is forced through the damaged valve in the wrong direction. This abnormal flow of blood can be heard by a vet as a heart murmur when they listen with a stethoscope.

Normal Heart Beat

Murmur Heart Beat


How do I recognise MVD in my dog?

There are two distinct phases of MVD; a long, silent phase where a dog with MVD shows no outward symptoms of there being a problem (the asymptomatic phase) and a shorter phase where the heart cannot cope and dogs show symptoms of their heart disease (heart failure phase).

Asymptomatic MVD

A dog with asymptomatic MVD will appear outwardly healthy and have no visible symptoms indicating a problem. The only symptom that will be detectable by a vet at this stage is a heart murmur. MVD is a slowly progressive disease that gets worse over time. A dog with MVD can live for many years without having any symptoms apart from a murmur.

Over time, the leak can get worse over time and as more blood flows the wrong way through the heart, the murmur gets louder and the heart is put under greater strain. To compensate, the heart becomes larger and pumps harder. Eventually, there comes a point when the heart cannot cope with the additional strain and fails to pump enough blood around the body. This is known as heart failure.

Heart failure

Symptoms of heart failure can initially be quite subtle. However as the disease worsens the symptoms become more severe as the heart’s function deteriorates.

Symptoms of heart failure include:

  • Increased breathing rate
  • Difficulty breathing
  • Tiredness
  • Difficulty exercising
  • Coughing
  • Fainting/collapse

Not all dogs with MVD develop heart failure.

Dogs with MVD who go into heart failure are those whose heart has enlarged as a consequence of their disease. Typically, dogs with both MVD and an enlarged heart will develop heart failure within 2 years.1

How is MVD Diagnosed by my Vet?

Cocker-poo with vet


When your vet examines your dog, they may find signs relating to heart disease. Listening to your dog’s heart with a stethoscope will allow a vet to detect a murmur and they may recommend further tests to establish if your dog has an enlarged heart.

There are two tests that your vet may use to determine if a dog with MVD has an enlarged heart:


A chest x-ray enables a vet to assess the overall size of the heart as well as checking for any fluid build-up in the lungs. Fluid in the lungs would indicate the presence of heart failure.


An ultrasound of the heart allows a vet to visualise and assess the inside of the heart, enabling them to take measurements to assess heart size.

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 would benefit from treatment
  • Provide you with an accurate prognosis
  • Monitor the progression of your dog’s disease

Both tests 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. This means that your dog has a lower risk of developing heart failure imminently.

However, it is important to remember that MVD is a disease that gets worse over time. Therefore, even if your dog’s heart is not yet enlarged, it is likely that your vet will recommend that he/she has these tests 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.

1 Boswood A et al. Effect of Pimobendan in Dogs with Preclinical Myxomatous Mitral Valve Disease and Cardiomegaly: The EPIC Study—A Randomized Clinical Trial. Journal of Veterinary Internal Medicine 2016;30:1765-1779.