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Heart Murmur in Dogs: Cause, Treatment, Symptoms And More

Last Updated - October 19, 2022

Listening to a dog's heart and lungs is an important part of every veterinary visit. But what if your vet hears something abnormal? It can be scary and overwhelming if your dog has a heart murmur.

There are many different types of heart murmurs and many possible causes. For example, an innocent heart murmur is not concerning and does not affect your dog's health, while others are due to much more serious underlying disease. Some dogs with heart murmurs have other symptoms of cardiac disease, but many do not. As a result, treatment and prognosis vary widely, but rest assured that many dogs with heart murmurs can live long, healthy lives.

Your vet will always remain the best source of information about your dog's heart murmur, but the following summary includes some key points that you should know. 

What is a Heart Murmur in Dogs? 

A heart murmur is a type of abnormal sound caused by turbulent blood flow through the heart. Your vet may notice a murmur when listening to your dog's heart with a stethoscope. While a normal heart makes a typical "lub-dub" as the heart contracts and relaxes to pump blood through the body, a heart murmur sounds less crisp and may have a "whooshing" quality. There are many different types and causes of heart murmurs in dogs, ranging in severity from completely benign to life-threatening, therefore treatment recommendations and prognosis vary widely.   

Types of Heart Murmurs

Heart murmurs can be classified in several ways. Classifying heart murmurs in this manner helps provide information about the severity and underlying cause of the murmur and thus helps guide treatment recommendations. 

Timing of Heart Murmurs

Heart murmurs are divided into three categories based on where in the heart cycle the abnormal sound is heard. 

  • Systolic murmurs: This common type of murmur is heard during systole, the phase in which the heart contracts to pump blood. Examples of systolic murmurs include mitral or tricuspid valve regurgitation, stenosis of the aortic or pulmonic valve, anemia, and cardiomyopathy. 

  • Diastolic murmurs: This is a rare type of heart murmur in dogs and is heard during diastole, the phase in which the heart relaxes to fill with blood. These murmurs are often associated with aortic insufficiency. 

  • Continuous murmurs: This murmur is heard continuously throughout both systole and diastole and is often associated with a birth defect in young puppies known as patent ductus arteriosus (PDA). 

Grades of Heart Murmurs

Heart murmurs are divided into six grades of intensity, based on what your vet hears through their stethoscope. In general, most innocent murmurs are grade 3 or lower; however, louder murmurs do not always indicate a poor outcome. Grading murmurs can be helpful upon initial diagnosis and provide a way to monitor a heart murmur's progression accurately. 

  • Grade 1: The softest heart murmur, which may be barely audible or only audible in a quiet room. 

  • Grade 2: A faint murmur that is easy to hear but may only be audible if the stethoscope is in a particular area on the chest.   

  • Grade 3: A moderate murmur that can easily be heard in multiple locations. 

  • Grade 4: A loud murmur that can be heard in multiple locations.  

  • Grade 5: A very loud murmur that can also be felt with the hands (palpable thrill). 

  • Grade 6: The loudest murmur with a palpable thrill and can also be heard when the stethoscope barely touches the chest.

Location of Maximum Intensity 

Heart murmurs sound the loudest or are sometimes only audible when the stethoscope is placed in a specific location on the chest. This correlates with the location of the chambers and valves within the heart. The spot where the murmur is best heard is useful in determining the underlying cause. Murmurs are generally classified as being loudest at the apex (the point or bottom of the heart) or base (the broad top part of the heart), and whether the murmur is best heard on the left or right side of the chest.  

Heart Murmur Configuration 

Heart murmurs are also divided into four groups based on how the sound quality of the murmur progresses, including plateau, crescendo-decrescendo, decrescendo, and machinery murmurs. 

Plateau murmurs: This type of murmur is uniform in loudness and may be associated with many causes of heart murmurs including classic mitral and tricuspid regurgitant murmurs. 

Crescendo-decrescendo murmurs: This type of murmur creates a noise that continuously changes between louder and quieter. It may be associated with aortic and pulmonic stenosis. 

Decrescendo murmurs: This type of murmur will start off loud and then become quieter over time. A classic example is aortic valve insufficiency.

Machinery murmurs: This type of murmur is often heard in patients with patent ductus arteriosus (PDA). 

All of this information is used by your vet to help them get a better idea of what is causing your dog's heart murmur and what steps to recommend next. For example, older small breed dogs often develop degeneration of the mitral valve, which causes the valve to leak and creates a characteristic left apical systolic murmur. 

Symptoms of Heart Murmurs in Dogs

The heart murmur itself is a symptom and is often found incidentally on physical exams. This means that the dog is otherwise healthy or seeing the vet for a different concern when the murmur is first noticed. Based on the underlying cause and severity, dogs with heart murmurs may have some of the following symptoms or be completely asymptomatic. 

  • Increased panting or respiratory rate at rest 

  • Exercise intolerance or tiring easily

  • Persistent cough

  • Pale, blue, or white gums

  • Distended abdomen due to fluid buildup

  • Fainting or collapse (syncope)

  • Abnormal heart rate or rhythm

  • Decreased appetite 

  • Heart failure 

  • Sudden death

What Causes Heart Murmurs in Dogs? 

There are many possible causes of heart murmurs in dogs. Some, known as innocent murmurs, are not concerning and have no effect on your dog's health, while others are more severe. These heart murmurs can be caused by an issue within the heart itself or a disease process elsewhere in the body. 

Innocent or physiologic murmur

These murmurs are often seen in puppies, are not serious, are generally low grade, and often resolve on their own by five months of age. They do not cause any clinical signs or progress to heart disease. 

Pathological murmur

A structural defect within the heart causes these murmurs. This may involve a leaky or damaged heart valve, weakening of the heart muscle, or an abnormal hole or vessel. These conditions have the potential to cause or progress to more serious heart diseases like congestive heart failure.

Extracardiac murmur

Conditions affecting other parts of the body, such as anemia, hypoproteinemia, fever, infection, hyperthyroidism, obesity or emaciation, and pregnancy, can also cause a heart murmur. Many of these conditions also have a variety of causes, ranging from mild to severe. 

Heart murmurs can be congenital, meaning they are present at birth (for example an atrial or ventricular septal defect), or acquired and can develop later in life. Two of the most common acquired causes of heart murmurs in dogs are mitral valve degeneration (degenerative mitral valve disease) and dilated cardiomyopathy.

Your dog's signalment (their breed, age, gender) can also provide important information about the cause of their heart murmur. Older small breed dogs are prone to developing a leaky mitral valve, while middle age large breeds are more likely to develop dilated cardiomyopathy.

How is a Heart Murmur Diagnosed? 

A heart murmur is an abnormal heart sound with many possible causes. The murmur itself is heard when a vet listens to your dog's heart with a stethoscope. If your vet hears a heart murmur, they will grade and classify it as discussed above. They will review your dog's history and perform a thorough physical exam to determine if any other signs or symptoms of heart disease are present and may recommend additional testing, including some or all of the following. Some of these tests may be done by your vet, or you may be referred to a cardiologist. 

Chest x-rays: Radiographs are a good starting point to help visualize the size and shape of the heart and look for evidence of fluid buildup in the lungs, which could be a sign of heart failure. 

Echocardiogram: A heart ultrasound allows a vet to see how effectively the heart is pumping and highlight areas with leaks or turbulent blood flow. This test can be critical in determining the underlying cause of a heart murmur. 

Electrocardiogram (ECG): A test to measure the electrical activity within the heart and evaluate heart rate and rhythm. 

Bloodwork, including heartworm test: Some markers of heart disease can be seen in bloodwork. Baseline blood work is also important for dogs beginning long-term medical management for heart disease. 

vet check up

Source: prexels

How is a Heart Murmur Treated? 

Depending on the severity and underlying cause, treatment recommendations will vary widely. Dogs with innocent murmurs will not need any treatment, and puppies often outgrow this type of murmur. Other types of heart murmurs may not require treatment initially but have the potential to progress to more advanced heart disease and/or heart failure. Therefore monitoring with routine vet visits is very important. If a murmur is severe and/or already causing signs of heart disease, then treatment, including medications, diet, and supportive care, may be indicated. Sometimes, surgery with a specialist is needed, especially in dogs with a congenital heart defect. 

Dogs whose heart murmurs are due to extracardiac causes will need to have their underlying disease addressed as well. Once this issue is treated, the murmur should resolve. However, these conditions also range from easily treatable to more severe. 

What Is The Prognosis Of a Heart Murmur? 

Prognosis depends greatly on the underlying cause and severity. The age and overall health of your dog will also play a role. While heart murmurs can be an overwhelming topic, many dogs go on to live normal healthy lives. If the underlying cause is more serious, discussing treatment options and long-term management with your vet will be important. 

FAQ

Can Heart Murmurs in Dogs be Prevented? 

A heart murmur is a symptom of an underlying issue and cannot be prevented in most cases. You can help keep your dog's heart healthy by using year-round heartworm preventatives, keeping their teeth clean with at-home dental care and dental cleanings under anesthesia with your vet, and feeding your dog a complete and balanced diet. Grain-free diets have recently been associated with heart disease in dogs. 

What is the Cost of Treating a Heart Murmur? 

Much of the cost associated with heart murmurs are due to diagnostic tests and monitoring, which will vary based on what is necessary for your individual dog, your vet clinic, location, and whether you are referred to a cardiologist. Long-term medication can also be costly in some cases, and your veterinarian will be able to provide you with a detailed estimate. 

About the Author

Liza C.

Liza is a veterinarian who graduated from MSU CVM in 2013 and spent five years working in small animal practice. She loved working with dogs and cats and educating owners on all aspects of veterinary medicine, especially animal behavior, and dermatology. She has since transitioned to remote work to be able to spend more time at home with her husband, two young kids, and two cats. She is thrilled to be able to combine her passions for veterinary medicine and writing. Liza is located in the Pacific Northwest and enjoys traveling, spending time at the beach, and family movie nights.

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