Mitral Valve Disease In Dogs

Quick Links

When a vet listens to your pet’s heart with a stethoscope, they can hear the sound of the heart beating as it pumps blood around the body. In a normal heart, the blood flows smoothly, and does not make any obvious noises. A “murmur” is heard when the blood flow is not smooth, but rather turbulent—like water over rapids, rather than a calm stream.

Murmurs are “graded” according to how loud they are. The quietest murmurs are grade one, and the loudest are grade six. In general, murmurs that are grades one or two are less worrying than those graded three or above.

Not all murmurs are caused by Mitral Valve Disease, so your vet cannot diagnose your dog just from listening with a stethoscope.

The mitral valve connects the two chambers of the left side of the heart. Its job is to make sure that blood flows straight through and out the heart, instead of going backwards. In order to do this, it must flex out of the way when the heart pumps, and then snap back and seal tightly closed when the heart is relaxing and refilling.

In some dogs, this valve will start to thicken and become stiff as they get older. This leads to leaking around the edges of the valve, meaning that some blood gets pumped backwards, rather than forwards. The leak causes turbulence in the blood flow, resulting
in a murmur that you vet can hear with a stethoscope.

Mitral Valve Disease is seen more often in smaller-sized dogs, particularly certain breeds such as Cavalier King Charles Spaniels, Chihuahuas, and Miniature and Toy Poodles. However, any breed or size of dog can be affected by this condition.

Almost all dogs with Mitral Valve Disease will have a heart murmur, but there are other conditions that can cause a murmur, too. In order to understand what is causing your dog’s heart murmur, your vet will need to arrange some further tests.

These tests may include:

Echocardiography (a “heart scan”)
Echocardiography uses ultrasound to examine the structure of your dog’s heart. This allows the vet to “see” the different chambers of the heart, and the valves, as well the flow of blood as it is pumped through. Based on this, a trained vet can diagnose the cause of your dog’s murmur, and see how advanced their condition is.

A heart scan is the only way to definitively diagnose Mitral Valve Disease. It can also be used to work out whether your dog will benefit from any treatment.

Heart scans are usually done without sedation, though sometimes the vet may recommend your dog has an anti-anxiety medication a few hours before their scan. The dog lies on their side on a table, and the vet shaves a small area on their chest (just behind their armpit) and places the ultrasound probe onto the skin.

Echocardiography is a specialized skill, and not every vet is trained to perform it. Your vet may recommend seeing a colleague, or going to see a cardiology specialist at a referral center.

X-rays
X-rays can be used to look at the outline of your dog’s heart, to see if there are any signs that it is becoming enlarged. An enlarged heart can be caused by Mitral Valve Disease, but there are other illnesses that can cause it, too. It can also look for signs of heart failure

Blood tests
Mitral valve disease cannot be diagnosed on blood tests alone, but there are some tests that can be used to try and measure how much strain the heart is under. This may be useful when trying to work out your dog’s risk of developing heart failure in the near future.

If your dog needs medication for their heart, your vet may also recommend some more general blood tests, too.

Electrocardiography (ECG)
Electrocardiography measures the electrical activity inside your dog’s heart. Electrical signals are used to tell your dog’s heart  when to beat, and changes in the heart can affect the way that this electricity flows through the muscles and nerves. ECGs are most commonly used when a dog has an irregular heartbeat, which can sometimes happen as a side-effect of Mitral Valve Disease.

If your dog has been diagnosed with a heart problem, then it is natural to worry about their condition getting worse. The first signs of a worsening heart problem can often be spotted at home:

Resting Respiratory Rate
The earliest sign that your pets heart may not be coping well is that they will start breathing more quickly, even when they are resting. You can monitor this by measuring how quickly your pet is breathing when they are resting at home. This is called the “resting respiratory rate”.

To measure this, choose a time when your pet is resting or sleeping. Using a watch with a second hand, or a timer on your phone, count the number of breaths that you pet takes in a minute. This is their “resting respiratory rate”.

A normal resting respiratory rate is:

• Up to 30 breaths per minute for dogs
• Up to 40 breaths per minute for cats.

You should measure your pet’s rate once or twice a week. If their rate is consistently higher than these levels, then you should arrange an appointment with your vet.

Lethargy
Another early sign that you pet heart is having trouble coping is that they are less active and not keen on exercise. This can show up in several different ways:

• Dogs may not manage to walk as far as normal, or may not want to go for their walks at all.
• Cats may not want to play, or may not go outside as much as they used to.
• Both cats and dogs may avoid stairs, or jumping or climbing on things.

There are other reasons besides heart disease that older pets can become less active, but if you notice anything like this then you should arrange an appointment with your vet.

Increased Effort Breathing
Both cats and dogs whose hearts are not coping well may find it more effort to breath than normal. Rather than just the chest rising and falling as they breath, their abdomen (belly) may move in and out as well. If you notice anything like this, contact your vet immediately.

Coughing
Dogs with heart disease may cough as part of their disease. Some dogs will cough regularly even with early heart disease; some dogs may only cough very little even with advanced heart disease. If you notice that your dog is coughing more frequently, or more violently than they used to, then you should make an appointment with your vet.

Cats with heart disease do not usually cough, so if they start to do so then you should contact your vet.

In the early stages of heart disease, pets may not need any medication. Sometimes, however, we may be able to give pre-emptive medication to try and prevent future problems, or keep you pets healthier for longer.

If you’re concerned your dog may have heart disease, or if they’ve already been diagnosed and you need guidance, we’re here to help. Contact your nearest practice today to speak with our caring veterinary team and ensure your pup gets the support they need. 

Our Latest News and Advice