Myxomatous mitral valve disease is one of the most common heart diseases for dogs. It usually affects smaller breeds (though can occasionally be encountered in middle-age or geriatric dogs, as well). Myxomatous mitral valve disease, which is also known as chronic mitral valve disease, mitral insufficiency, endocarditis, degenerative mitral valve disease, or simply MMVD, can also affect cats, though very rarely.

It is yet unclear what causes myxomatous mitral valve disease, but it is thought to be a complex process that leads to the degeneration of the mitral valves (on the left side of the heart, between the atrium and the ventricle). What happens in MMVD is that the valves thicken and detract, which in time creates a hole through which blood can go back from the ventricle into the atrium. This leads to the mitral chordae tendineae tearing, which causes the valve to flop, without sealing the left atrium off properly. In time, if MMVD becomes serious enough, it can cause congestive heart failure.

MMVD is a fairly common disease, affecting roughly 10% of smaller breed dogs, in their old age. One breed that’s particularly affected by MMVD is the Cavalier King Charles spaniel, who also happens to develop MMVD at a fairly young age (about four years old). Though common, the disease progresses slowly in most dogs, and 75% of affected dogs usually die of something else. Still, that doesn’t mean MMVD should be ignored or overlooked.

Signs of MMVD

Unfortunately, MMVD usually goes undetected by the owner, and will only pop up during a vet check-up, even when you thought there was nothing wrong with your dog. That’s because most dogs affected by mitral valve disease don’t exhibit any clinical signs, during the milder stages of the disease. The only possible warning sign is a murmur felt when picking up your dog as if your dog were purring. That’s the leak on the left side of the chest, caused by MMVD.

Dogs with MMVD may, occasionally, faint. Though harmless, this fainting can scare the owner, and is one of the first signs of congestive heart failure. The good news is, that it can be controlled with corrective measures.

As congestive heart failure develops, your dog may also experience pulmonary hypertension (with symptoms like shortness of breath, and right-sided CHF, alongside the fainting).

Diagnosis of MMVD

Your veterinarian will take into account multiple factors while diagnosing MMVD, such as the age, and size of your dog, alongside the presence of the left-sided murmur. If your dog is an older small-breed with a murmur, then an MMVD diagnosis is quite likely.

Of course, identifying mitral valve disease is just the first step of the process, which then needs to be followed by determining how severe the affliction actually is. In order to do this, your vet will need to perform X-rays on your dog’s chest, to examine the size and condition of your dog’s heart and lungs. If in doubt, your vet may also perform an echocardiogram, to determine an accurate diagnosis.

The severity of the disease refers to how much blood is leaking between the valve and the atrium. By measuring the left atrium, your doctor will be able to determine the severity of your dog’s MMVD.

This will show up on chest X-rays, though not always, since mild MMVD shows no enlargement, moderate MMVD visible, though not overwhelming enlargement, and severe MMVD shows signs of marked cardiomegaly. It is only in the severe stages of MMVD that congestive heart failure sets in since the leak is acute.

MMVD Treatment

Naturally, the specific treatment for MMVD will depend on how advanced the disease is – subclinical and congestive heart failure CHF). During the subclinical phase, the primary focus is on slowing down the degeneration and reversing the process, so as to avoid congestive heart failure.

This is typically done by the use of retardants (angiotensin-converting enzyme inhibitors also known as ACE-inhibitors, pimobendan, and spironolactone), which are drugs that slow down the progression of the disease. Pimobendan is highly efficient in delaying the onset of CHF, though treatment is recommended only when the heart is visibly enlarged, so as to avoid needless treatment too early. Your vet may also prescribe a sodium-free diet, though there’s limited evidence of its efficiency.

The treatment of CHF in dogs with MMVD is more complex. Diet plays an important role in CHF treatment, with owners being advised to avoid high salt content treats (including human foods, like deli meats, chips, cheese, and so on). If you’re using people’s foods to conceal pills or meds, try switching to things like no salt added peanut butter, instead.

Avoiding excessive exercise may also be advisable, particularly if it puts a strain on your dog’s heart, or leads to panting or weakness.

Surgery for MMVD?

While it’s not uncommon for humans with mitral valve disease to undergo replacement surgery, such procedures are still in the experimental stage for dogs. Inserting prosthetic valves to reduce the size of the leak is rapidly becoming an option, with cardiovascular surgeons performing such procedures on dogs in the UK, France, and Japan. Unfortunately, since it is only an experimental procedure, the costs are quite high (roughly around $40,000), which makes it too expensive for most dog owners. If interested, we recommend contacting such programs directly for more details.

Monitoring MMVD progression

Depending on how advanced the MMVD is, your vet will schedule check-ups to monitor the disease’s progression. For mild cases, a check-up might occur in a year’s time, while for more severe cases, they can be more frequent. These will monitor the dog’s breathing rate. You should also keep an eye on that – if your dog’s breathing quickly during sleep, it might be a good idea to see a vet asap.


While most dogs with MMVD won’t even develop heart disease, those who do get CHF are likely to die from it, with 50% of studied dogs dying from CHF in 9-10 months from diagnosis. A whopping 80%, unfortunately, die within 18 months, and very few survive more than 2 years after the diagnosis.