Mitral valve disease in dogs is the most common canine heart disease veterinarians see, making up 75 percent of all canine heart problems. It’s also known as degenerative mitral valve disease (DMVD), and myxomatous mitral valve disease (MMVD). Although estimates vary from study to study, it’s estimated that about 3.5 percent of all dogs attending a veterinary practice will have mitral valve disease at any one time, with the incidence increasing as dogs age. 

Because it’s so common, it’s important to know what this disease is and how veterinarians treat it. Let’s discuss mitral valve disease in dogs in more detail. 

What Is Mitral Valve Disease?

Mitral valve disease (MVD) in dogs is a disease of the heart. The mitral valve is a valve that sits between the left atrium and the left ventricle to prevent a backflow of blood when the heart contracts. It changes shape due to the disease, meaning it doesn’t fit the space properly. 

Instead of preventing a backflow of blood, the thickened, misshapen valve leaks, causing blood to flow back the wrong way. This is why the condition is sometimes called mitral valve regurgitation. Veterinarians can hear this backflow with a stethoscope as a heart murmur.

This backflow of blood causes problems. It means the atrium isn’t empty when new blood enters, so less blood can fit in. Because less blood is being pumped, a dog’s heart has to pump faster to get the same amount of blood around the body, which causes the heart to grow larger, taking up more space in the chest. Because less blood can fit in the atrium, there’s a build-up of blood returning from the lungs. Even though the atrium grows in size to accommodate the excess blood, the backlog eventually causes fluid to accumulate in the lungs. This is called congestive heart failure, and it’s the end stage of mitral valve disease.

Mitral valve disease in dogs is a degenerative change that happens as pets age, so it’s more common in older dogs. Some dog breeds are more prone to MVD and may get degenerative heart changes and a heart murmur earlier in life. It’s most common in dogs under 44 pounds – however when dogs over 44 pounds are affected, they have a worse prognosis. It’s also more common in males than females, although we aren’t sure why.

Causes of Dog Mitral Valve Disease

Mitral valve disease is a degenerative disease – it gets worse over time, with the valves slowly becoming more thickened and less able to control the flow of blood. We don’t know entirely what causes mitral valve disease in dogs, but there are several contributing factors. 

Genetics definitely play a large part, as is seen with some breeds being more affected than others. Breeds at higher risk of mitral valve disease include:

• Cavalier King Charles Spaniels
• Miniature Schnauzers
• Miniature Poodles
• Shih Tzu
• Maltese
• Cocker Spaniels
• Chihuahuas
• Pomeranians

As well as breed and genetics, we know that some other things are associated with a higher risk of MVD in dogs. Bacterial infection of the heart valves (called endocarditis) is one thing that increases the risk of mitral valve disease in dogs. While severe endocarditis is rare, some diseases, like periodontitis – a common dental infection – can introduce bacteria to the blood that can damage the heart valves.

Symptoms of Mitral Valve Disease in Dogs

The first symptom of mitral valve disease in dogs is usually a heart murmur. This is usually not audible without a stethoscope, so you may not realize your dog has a heart murmur until a routine visit with your veterinarian. 

As your dog progresses through the stages of MVD, they will get more symptoms. These include:

• Heart murmur (as this worsens, you may be able to hear it without a stethoscope)
• Coughing (especially when your dog gets up after resting, or at night)
• Lethargy
• Reluctance to exercise
• Breathlessness/fast breathing
• Difficulty breathing
• Weight loss
• Fainting and collapse

Diagnosing Mitral Valve Disease in Dogs

In a small breed dog who is getting older, mitral valve disease is highly likely, so if your vet hears a murmur during a routine examination, they will often make a presumptive diagnosis. For treatment purposes, a definitive diagnosis and disease staging is useful. 

Your veterinarian will need to run blood tests, take your dog’s blood pressure, and will recommend an ultrasound, an X-ray, or both. This heart ultrasound may need to be done by a specialist, so you may be referred to a cardiologist to have these tests completed. 

Not only do these tests confirm that your dog has mitral valve disease (rather than another heart disease of dogs), but working out the stage of the disease allows vets to decide when to start treatment, and which medications to use.

Stages of Dog Mitral Valve Disease in Dogs

When diagnosing mitral valve disease in dogs, vets will diagnose a ‘stage’ of the disease. These stages are labelled A-D, and are based on which clinical signs are present. They were suggested by the world’s top canine cardiologists in the ACVIM consensus and are very useful for planning treatment. 

Dogs start at a lower stage (A or B), and progress through the stages as their disease worsens, with stage D being the last – and most severe – stage. Let’s look at the stages of MVD in more detail:

Stage A

Stage A dogs are those that are at high risk, but who don’t currently have abnormalities. They don’t have a heart murmur, and there would be no changes on heart ultrasound or on an x-ray. Every dog in the high-risk breed list above can be considered to have stage A mitral valve disease. 

Stage B

Stage B describes dogs that have physical changes from mitral valve disease (which may result in a heart murmur), but that have not had symptoms of heart failure. These dogs will usually have had a heart murmur picked up on a routine exam. If further investigations into these murmurs are undertaken, stage B dogs can also be separated into two further categories – B1 and B2. 

• Stage B1 describes dogs that have a murmur and no physical changes to their heart shape or size.  It can also include dogs with a heart murmur that have very minor changes to their heart shape or size.
• Stage B2 describes dogs that have a murmur and significant changes to heart shape or size. 

This separation has come because the results of a clinical trial suggested that medicating dogs in the B2 category can help – if your dog’s heart changes meet a set of predetermined criteria, the benefit of medication is higher than the risk, and your vet will recommend they start treatment. These dogs are still stage B though, as they haven’t yet had heart failure symptoms.

Stage C

Dogs in stage C have a heart murmur, physical changes to their heart, and have (or have had in the past) symptoms of heart failure, such as coughing. These symptoms don’t have to be current, because dogs may have been started on treatment and the symptoms have lessened or temporarily disappeared. However, it’s important to remember that this is a progressive disease – despite initial good response to treatment, all dogs will eventually have further episodes of congestive heart failure.

Stage D

Stage D dogs have all of the above, but their heart failure is now so severe that standard treatments are no longer effective. Advanced or even surgical treatments are now necessary to maintain the dog’s quality of life. This is end-stage mitral valve disease in dogs, and at this point you will need to carefully monitor your dog’s quality of life and consider euthanasia when it becomes poor.

Mitral Valve Disease Treatment and Management for Dogs

It’s important to understand that dog mitral valve disease will progressively get worse, even with treatment. However, treatment can slow the progression of the disease, as well as give your dog a better quality of life for longer. The type of treatment your dog requires will depend on the stage, with treatment recommendations starting at Stage B2. 

Treatment for Mitral Valve Disease Stage A

Your dog will not need any treatment, but you may request regular monitoring or screening as they get older..

Treatment for Mitral Valve Disease Stage B1

No treatment is indicated for dogs with stage B1 MVD, but it’s recommended you carefully monitor them at home and that X-rays/ultrasounds are repeated in 6-12 months. 

Treatment for Mitral Valve Disease Stage B2

At this stage, your vet will start to recommend some low-risk treatments. This includes changing your dog’s diet to a low salt option, ensuring that it has enough calories and protein to help your dog maintain their weight as the disease progresses. 

A medication called pimobendan may also be recommended – this will need to be given twice daily for the rest of your dog’s life. Regular measurements of your dog’s resting breathing rate can offer an early warning system for heart failure. 

Treatment for Mitral Valve Disease Stage C and D

As dogs progress to stage C and D, other drugs are added to the mix. Alongside pimobendan, your dog may be prescribed furosemide, torsemide, spironolactone, benazepril, digoxin, or amlodipine. Omega fatty acids may also be recommended. 

You will need to carefully monitor your dog at home, ensure they eat properly, and keep good track of their medications. They may need to be admitted to the hospital for oxygen therapy and high-dose injectable drugs in severe episodes. Once these episodes have quietened back down, your dog can usually return home with adjustments to their medications. 

At these later stages of canine MVD, your dog will usually be visiting the vets every couple of months for monitoring visits.

Surgery for Dogs with Mitral Valve Disease

Recently, mitral valve repair and replacement surgeries have been trialled on dogs, with some good success. There are a few specialist centers in the world that can repair or replace the mitral valve in dogs. It’s generally used in dogs of stage C or more, as this surgery obviously has significant risks, but some stage B2 patients may also be eligible. You will need to be prepared to travel, often a long distance, to get heart surgery for your dog, and your dog needs to be well enough for the journey. 

Mitral Valve Disease in Dogs: Life Expectancy

The average life expectancy of a dog with mitral valve disease is just a year once dogs are in stage C.

Every dog is different, and they will go through the stages of mitral valve disease at different rates. Small dogs tend to progress through the stages more slowly than large dogs, who can have a far worse prognosis. 

Cost to Treat Mitral Valve Disease in Dogs

As mitral valve disease is progressive, costs will increase over time as more and more treatments are necessary. To begin with, investigations into a murmur heard at a routine examination are likely to cost $300-$700, depending on exactly which tests are necessary. This should be covered by your dog’s insurance, as long as you took out the policy before your vet heard the heart murmur. 

Once dogs are into stage C, the huge variety of drugs they require, plus regular consultations to ensure they’re getting the right dose, can quickly add up. Budget $50-$150 per month, with money in reserve for a hospital stay. Luckily, insurance policies should also cover this stage, although with some time-limited policies, your time might be up before your dog reaches this more intensive (and expensive!) stage of treatment.

Surgery is extremely expensive, as it’s a specialist procedure requiring many highly trained personnel, extensive monitoring, and complex equipment that is expensive to maintain. This sort of procedure is well beyond most insurance policies, coming in at around $30,000. You’ll also need to factor in travel to the surgery and an extended stay, especially if they don’t operate in your country.

How to Prevent Mitral Valve Disease in Dogs

Unfortunately, there’s not much you can do to prevent mitral valve disease in dogs. Keeping your dog’s teeth clean will reduce the risk of bacteria in the blood damaging the heart valves. While this may help some cases however, it isn’t the main cause of MVD, and many dogs will get the disease despite having good teeth. Scheduling regular check-ups with your veterinarian should lead to early diagnosis, meaning you can start treatment as soon as it’s indicated. You should also consider only buying puppies from parents who are regularly undergoing heart checks, especially if you’re purchasing a puppy that belongs to a breed predisposed to MVD.

Conclusion

MVD is a common, life-limiting disease that steadily gets worse over time. It’s unpredictable how fast dogs move through the stages of MVD, with some dogs staying in stage B1 for a very long time, meaning they can have a great quality of life with little to no interventions. 

Once dogs have signs of congestive heart failure, interventions increase, costs increase, and their prognosis becomes poorer.