What is a heart murmur in dogs?

Heart murmurs refer to an unusual sound that’s detected when listening to a dog’s heartbeat through the stethoscope. Instead of the regular heart sounds, there may be a ‘whooshing’ noise indicating an abnormal blood flow through the heart. Heart murmurs in dogs vary in severity, from manageable to life-threatening. 

So, it’s important to talk to your vet about your dog’s symptoms to determine what type of medical help is needed. Keep reading to find out the key signs to look out for.

• Coughing.
• Lethargy.
• Excessive panting.
• Fainting.
• Pale gums.
• Getting tired quicky.

Some dogs with a heart murmur will not show any signs of heart disease but if you notice any of these unusual symptoms, get in touch with your vet straightaway. They will be able to assess your dog’s condition and, if a heart murmur is detected, they will let you know the type, grade and the most effective treatment, to increase the likelihood of your dog getting back to their usual, happy self.

The 6 grades of heart murmurs in dogs:

Grade I

Grade I hear murmurs are the quietest ones on this scale. They are barely audible and usually the least serious. Your vet may decide to monitor a grade 1 murmur, or they may advise investigations.  

Grade II

These murmurs are slightly more audible, but still soft in intensity.

Grade III

Grade III murmurs are more easily detected through the stethoscope and may point to conditions that are serious.

Grade IV

Grade IV murmurs are easy to hear with a stethoscope and are somewhere between grades III and V in intensity.

Grade V

Heart murmurs that are so loud they can be felt by resting your hand against the dog’s chest are classed as Grade V. The vibrations that you may feel as the heart pumps are known as a ‘thrill’.

Grade VI

The most intense murmurs are often a sign of significant heart disease. Your vet may be able to hear a Grade VI murmur through their stethoscope without even placing it directly on the chest. Sometimes grade VI murmurs are so loud that they can even be detected without the help of a stethoscope.

Determining how loud or quiet your dog’s heart murmur is, will help the vet come up with a diagnostic plan. But another important part of the consultation is understanding what type of murmur your dog is experiencing.

Types of heart murmurs

The vet will listen the dog’s heart through a stethoscope to determine when the murmur occurs, how long it lasts and what part of the heart it’s coming from.

The murmur can appear when the heart muscle contracts (systolic murmurs), in between heart beats when the muscle is relaxed (diastolic murmurs) or they can appear continuously throughout the heartbeat cycle. They can also be long or short, start loud and get quieter or manifest in a crescendo.

All these details are important in establishing what exactly is causing the abnormal noise in your dog’s heartbeat.

What causes heart murmur in dogs?

You might think that heart disease is the cause behind the unusual heartbeat sounds. Although this is often the case, there are other possible conditions leading to heart murmurs. Here are some of the possible causes of heart murmurs:

• Anaemia.
• Pregnancy.
• High temperature.
• Hyperthyroidism.
• Heart issues including cardiomyopathy, endocarditis or damage to the heart valves.
• Heartworm disease.

Heart murmur in puppies

Puppies can also experience heart murmurs. This can happen in all shapes and sizes of pups including large breed puppies. Many puppy heart murmurs are what is called innocent flow murmurs or physiologic heart murmurs. They are low in intensity (so can only be detected by your vet with their stethoscope) and don’t usually require medical intervention. Innocent flow murmurs in puppies often disappear completely before the pup is six months old. However, you should always check with your vet to make sure the unusual heart sound is just a harmless part of growing up and not a medical condition that needs urgent attention.

In rare cases, your puppy might have a heart murmur as a result of a congenital heart problem. These are often (but not always) quite loud heart murmurs. They will almost always require investigation and are likely to require both regular monitoring and medical or even surgical intervention.

How are heart murmurs treated?

If the heart murmur is low in intensity, the vet may recommend close monitoring with or without medical treatment. Physiologic murmurs in puppies will often resolve on their own. Where necessary, your vet will recommend a treatment plan for the underlying condition, whether that is anaemia, hyperthyroidism or heart disease. So, the treatment will differ based on what exactly is causing the unusual blood flow through the heart.

Make sure you follow your vet’s instructions and continue to look out for any new symptoms. In many cases heart murmurs in dogs will not stop your pet living a long and happy life. Remember that prompt intervention is often key to keeping your pet well, so don’t forget about the regular vet visits with your dog.

Next, check out other reasons why your dog might be coughing with our guide.