Emergency 087 1318706
Southview Veterinary Hospital - Small Animal 052 6121429
Southview Veterinary Hospital - Farm 052 6121429


Myxomatous Mitral Valve Disease

What is MMVD?

MMVD is a common acquired heart disease which frequently affects smaller breed, older dogs, though it can affect large breed or younger dogs on occasion. This disease may also be called degenerative mitral valve disease (DMVD), mitral valve endocardiosis, or chronic valvular insufficiency.

Stages of MMVD:

MMVD occurs when the mitral valve, on the left-hand side of the heart, becomes damaged or defective. In some cases, the tricuspid valve on the right-hand side may also be affected. Damage to the mitral valve causes blood to leak backwards into the left atrium every time the heart beats (Stage B1). This eventually causes enlargement of the chambers on this side – the left atrium, and then the left ventricle (Stage B2).

As time goes on, blood pressure will begin to rise within the veins leading back to the lungs, and fluid leaks from the blood vessels into the lung tissue (“pulmonary oedema”) (Stage C). Additionally, the drop in cardiac output causes a neuro-hormonal response to be triggered in the body. This causes fluid retention by the kidneys, an increased heart rate, and increased blood pressure. Whilst this response is helpful in the short term, over a longer period this causes excess fluid retention and deterioration in the heart’s ability to pump.

When these factors combine, they lead to a condition known as congestive heart failure (CHF) - All pets in Stage C MMVD are in CHF. It is only at this stage that clinical signs are usually noticed by the owner. End stages of MMVD occur when the disease cannot be adequately controlled despite appropriate treatment (Stage D). These patients develop severe congestion or other complications which cause a decline in quality of life and ultimately, death.

Symptoms/Clinical Signs

The only detectable symptom of MMVD in its early stages (stage B1 & B2) is development of a murmur on the left side of your pet’s heart. Symptoms only develop in later stages (stage C and D). The most common symptom seen is a change in your pet’s breathing. Initially this may just present as a faster breathing rate (“tachypnoea”); but it can also lead to laboured breathing and severe respiratory distress (“dyspnoea”).

Coughing is seen in some patients, but not all.

Exercise intolerance is another common symptom, and some pets also develop episodic weakness or

When the tricuspid valve is also affected, it can cause fluid accumulation in the abdomen (ascites) or
chest cavity (pleural effusion).


The most important diagnostic test for patients suspected to have MMVD is echocardiography (also called an “echo” or a heart scan). This is where ultrasound is used to examine the heart. It is the only way to confirm both the diagnosis and stage of the disease. Echo is non-invasive and very well tolerated by most pets, therefore sedation is generally not needed for this test to be performed.

Additional tests may also be recommended, including chest X-rays - to diagnose fluid on the lungs, and to assess the presence of concurrent lung disease - and ECG, to check for arrhythmias.


MMVD is often a slowly progressive disease in its earlier stages, taking several years from the onset of the valve leaking and development of clinical signs, with some dogs never developing clinical signs. However, if congestive heart failure develops, it can be rapidly fatal without appropriate treatment – but with careful medical management, patients with CHF can still achieve a good quality of life for several months, or sometimes, years.


Treatment of early MMVD (Stage B2 Disease)

It has been proven that starting a medication called pimobendan during Stage B2 of MMVD can significantly extend the amount of time it takes to reach congestive heart failure. The trade names for pimobendan include Cardisure and Vetmedin.

The good news is that for many patients, this means we can keep them free of clinical signs for several years. However, it is very important to recognise the signs of heart failure developing, and to seek veterinary attention as soon as possible if they occur.

You may be asked to monitor sleeping respiratory rates alongside more obvious breathing or energy
changes to try to recognise CHF developing as early as possible.

Treatment of later MMVD (Stage C Disease)


  • Pimobendan (Vetmedin/Cardisure): This drug is very important for pets in CHF. It helps to improve lifespan by improving heart contractility and minimising the workload on the heart.
  • Diuretics (Furosemide): Diuretics are vitally important for pets in CHF. These are drugs which remove excess fluid from the chest or abdomen. These will keep your pet breathing comfortablyand to avoid a respiratory crisis from occurring. Furosemide is the name of the most commondiuretic used. They will cause your pet to urinate more and drink more water than before.
  • Other drugs may be recommended to counteract heart remodelling and slow down progression of disease; these include spironolactone and ace inhibitors (such as benazepril/ “Fortekor”).

Sometimes complications such as pulmonary hypertension or arrhythmias also occur alongside MMVD, and these may require additional treatment also.

Surgical repair of the mitral valve is an alternative to medical treatment. Currently this is very expensive and is only being performed by a handful of centres worldwide. Please enquire if you would like more information on this option.

It is important to monitor pets on treatment in case adjustments are needed to their drug dosages. You may be asked to monitor sleeping respiratory rates, as well as attend the clinic for repeat check-ups at certain intervals, especially if there has been a recent change to your pet’s medication.

Return to Cardiology