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Heart Murmur In Dogs: Symptoms And Life Expectancy | BetterVet

As pet parents, we want our furry family members to be as healthy and happy as possible. So, if we get the dreaded news that something might be wrong with their health, it can be a scary time. What if you’re all prepared for your perfect puppy but the vet hears a heart murmur? Or what if your vet finds a heart murmur at your golden oldie’s booster shot appointment? Let’s find out what causes heart murmurs in dogs and what to expect if your dog has one.


What is a heart murmur in dogs?


A heart murmur is when the flow of blood through the heart is more turbulent than it should be. If your dog has a heart murmur, the vet will be able to hear a ‘whoosh’ type noise while they’re listening to your dog’s heart with a stethoscope. Heart murmurs can be graded by how loud they are, from a grade 1 (I) murmur which is barely audible to a grade 6 (VI) murmur which is so loud it can be heard with the stethoscope lifted slightly.


What sound should a normal heart make?


A normal dog's heartbeat should sound like a steady 'lub-dub, lub-dub’ sound, just like a human’s. The lub is the sound of the valves closing between the atria and ventricles. The dub is the sound of the semilunar valves closing to prevent blood from flowing back into the heart. The speed of a normal dog's heartbeat will vary between big dogs and small dogs (small dogs have a faster heart rate) but the basic sound is the same. If your dog has a heart murmur, depending on the cause, it could be before, after, or in between the lub dub.


What causes a heart murmur in dogs?


There are lots of reasons why your vet might be able to hear a heart murmur. Here are some of the most common causes:


Physiological or ‘puppy murmur’


The thickness or viscosity of a puppy's blood is different from an adult dog. This, combined with the fact that the heart is growing rapidly, can lead to turbulent blood flow and a murmur. Puppy murmurs are usually quiet and disappear by six months of age. These physiological murmurs are innocent puppy murmurs and will not make your puppy unwell. It is important to follow up with your veterinarian as your puppy grows up to ensure the murmur goes away. 


Leaky heart valves


There are two sets of atrioventricular valves that lie between the atria and the ventricles. They prevent blood from flowing back up into the atrium when the ventricle contracts. If they don’t form a good seal, blood leaks through the gaps. This jet stream of blood causes the murmur sound. An example of this is Mitral Valve Disease (MVD), which is common in small breed dogs and particularly prominent in Cavalier King Charles Spaniels.


Birth defects


If the heart and surrounding blood vessels don’t develop properly before birth, this can lead to a heart murmur. These congenital abnormalities could lead to extra blood vessels, a hole in the heart, or a narrowing of a blood vessel. Patent Ductus Arteriosus (PDA) is an example of an additional blood vessel. The ductus arteriosus is a vessel that bypasses the lungs when a puppy is in the womb. When the puppy is born, the vessel should close. However, occasionally it doesn’t. 

Another example of a congenital condition is Pulmonic Stenosis, where the pulmonic valve forms a partial obstruction so that the blood cannot easily leave the heart to go to the lungs. These conditions can be very serious, and without prompt treatment, can be life-threatening. 


Changes in the size of the heart


If the heart becomes enlarged, the blood flow becomes more turbulent and less smooth. This can lead to murmurs, although it doesn’t always. Dilated Cardiomyopathy (DCM) in dogs causes enlargement of the heart and thinning of the muscular walls. This condition is common in Dobermans and Cocker Spaniels, among other breeds, and sadly can be fatal. It’s important to remember though that DCM doesn’t always cause a heart murmur, so dog breeds who are predisposed should be screened for the condition.


Can a heart murmur be treated?


Some causes of heart murmurs can be treated, while others can’t. As a rule, congenital heart murmurs are more treatable than heart murmurs acquired later in life. For instance, a veterinary cardiac surgeon can close a PDA or widen a narrow valve using a small balloon. For acquired murmurs associated with MVD or DCM, the condition cannot usually be cured, but medication can be used to control the signs of heart failure and help the heart to pump more effectively for as long as possible. Thankfully, medication has now been shown to be effective at delaying the onset of symptoms if started early, so speak to your veterinarian about treatment options if your dog has a heart murmur.


What are some of the signs of heart failure in dogs?


Dogs with heart failure often develop a soft, moist cough that becomes gradually more frequent. You might also notice that they’re not able to exercise as much as they used to, they’re panting more, or they tire easily. If you’re particularly observant, one of the first signs is an increase in your dog’s breathing rate when they’re at rest. So, if your dog has a heart murmur, it’s worth getting to know their normal resting breathing pattern. As congestive heart failure progresses, it can cause the gums and tongue to become pale or blueish, and fluid might develop in their belly, giving them a bloated appearance. They might also have episodes of collapse and even lose consciousness.




What should I do if my dog is showing signs of heart failure?


If your dog is showing signs of heart failure, even if you’re unaware of them having a heart murmur, it’s best to schedule a visit with your veterinarian immediately. They may require medication, and it could help save their life. On the other hand, even if it isn’t heart failure, there could be another health condition causing the symptoms that should still be checked out. 


When should I worry about my dog having a heart murmur?


A heart murmur doesn’t mean that your dog has heart failure, nor does it mean that they’ll develop heart failure soon. What’s most important is that it is monitored closely by your vet and that you know what symptoms to watch out for.


Can a dog live with a heart murmur for a long time?


The prognosis for a heart murmur will vary depending on the cause. Many birth defects can become fatal without treatment. However, heart murmurs in adult dogs can remain stable without treatment for years before congestive heart failure begins. Acquired conditions like MVD can be managed with diuretics and other medications to control your dog’s blood pressure and help the heart pump more effectively. While these sadly won’t work forever, they can give you many months or even years with your canine companion.



It’s always stressful when you’re told that your pet has a health condition. But, if your dog has a heart murmur, try not to panic. There are many different causes and there are often treatment options available to help manage the condition long-term. Most importantly, speak to your vet if you have any questions or concerns about your pet's heart murmur as they can reassure and advise you as to the best course of action going forward