Heart Murmur in Dogs: Why You Shouldn’t Wait To Take Action

By Chelsea Hunt-Rivera / April 23, 2018

Imagine sitting at your veterinarian’s office as the doctor listens to your dog’s heart. Your doctor takes off their stethoscope and starts explaining the definition of a heart murmur in dogs.

It would be hard not to panic. We all know how vital the heart is and now there’s potentially something very wrong with it. It’s a terrifying thought, to say the least.

Before you break out into total panic mode, there are a few things you should know about heart murmur in dogs. It may not be as horrible as you think.

dog with heart murmur

What is a Heart Murmur in Dogs

A dog’s heart, like most living creatures’ hearts, pumps blood through the blood vessels of the circulatory system.

Heart murmurs are extra heart vibrations. These extra vibrations indicate a disturbance in the blood flow. Typically, the disruption occurs when the blood in the dog’s heart flows too rapidly out of normal and abnormal valves.

In fact, the extra heart vibrations create a disturbance so strong that it’s able to cause an audible sound.

dog's heart murmur

While a heart murmur itself is not a disease or disorder, it can be a tell-tale sign of heart trouble. Heart issues such as endocarditis, abnormalities in the valves, or stenosis (the narrowing of the arteries), as well as heart disease, can be underlying issues.

Murmur Definition

A murmur is a soft, indistinct, recurring sound that is often indicative of disease or damage.

Types of Heart Murmurs

There are three types of heart murmurs in dogs. A veterinary cardiologist classifies it based on the timing of the murmur. Knowing what type of heart murmur your dog has helps determine what is causing the murmur.

Systolic Murmur

The majority of heart murmurs are systolic. Systolic murmurs occur during a phase called systole. In the systole phase, the heart muscle contracts to pump out blood.

Diastolic Murmur

Diastolic murmurs occur when the heart is relaxed. The murmurs happen in between heartbeats.

Continuous Murmur

Conversely, continuous murmurs happen throughout the dog’s normal heartbeat cycle.

Heart Murmur Grading Scale

Grading heart murmurs is another way that veterinarians diagnose the condition.

Heart murmurs are graded on a scale from one to six. They are not necessary graded by severity, but more so as a grouping system. The grades serve as a way for a veterinary cardiologist to further categorize the murmur.

Grade I

These murmurs are barely detectable, even with a stethoscope. They are the least dangerous murmur on the grading scale.

Grade II

Murmurs are soft, but easily heard with a stethoscope.

heart murmur

Grade III

Most murmurs in the Grade III category (and further progressed murmurs) develop from problems related to the mechanics of blood circulation. Murmurs that cause serious issues are at least a Grade III. They have an intermediate loudness that is easily detectable.

Grade IV

Murmurs are loud enough that they are able to be heard from the other side of the chest due to it radiating so broadly.

Grade V

Murmurs are very loud. They can physically be felt by holding a hand up to the dog’s chest.

Grade VI

Murmurs are incredibly loud. Some murmurs can ever be heard without a stethoscope. The vibration is easily felt by hand through the chest wall.

Configurations of Heart Murmurs

Outside of the six grades, there are four main categories of configurations (sometimes called qualities) that a heart murmur can have. Determining the configuration of the heart murmur is the veterinarian’s next step in figuring out what underlying issue is causing the heart murmur.

Plateau Murmurs

These murmurs usually have a uniform loudness, meaning that they maintain a relatively consistent intensity. Plateau murmurs are most often congruent with an aortic valve insufficiency.

Crescendo-Decrescendo Murmurs

Murmurs that are categorized as crescendo-decrescendo behave in the way that the name describes: They get louder and then quieter. Most often, crescendo-decrescendo murmurs are associated with aortic and pulmonic stenosis.

Decrescendo Murmurs

These murmurs start of loudly and then get quieter. They are characteristic of diastolic murmurs. Decrescendo murmurs are often seen in dogs with an aortic valve insufficiency or a ventricular septal defect.

Machinery Quality or Continuous Murmurs

These murmurs are associated with a congenital heart defect known as patent ductus arteriosus (PDA). They are most often caused by blood flow from a high-pressure chamber to a lower pressure system.

Heart Murmur Symptoms

heart murmur symptoms

The symptoms of heart murmurs vary on a number of factors including their grade, configuration, and location. They will also vary in severity depending on how the murmur is categorized.

While some dogs do not display any physical symptoms of having a heart murmur, others will show signs.

For example, dogs with heart murmurs that are associated with structural heart disease may have symptoms of congestive heart failure.

Conversely, a physiologic or innocent heart murmur does not show any clinical symptoms or signs of the murmur existing.

Congestive Heart Failure Symptoms

Pet owners should be aware of the clinical signs of congestive heart failure as structural heart disease and heart murmurs have a strong correlation.

The most frequent clinical sign of congestive heart failure is persistent coughing along with heavy breathing. These symptoms are generally always caused by an accumulation of fluid in the lungs or a pulmonary edema.

The persistent coughing can also be due to the dog’s enlarged heart pushing against the trachea.

Other symptoms of congestive heart failure that can also be clinical signs of a heart murmur are:

  • Coughing at rest
  • Weakness
  • Quickened breathing rate
  • Difficulty catching its breath
  • Fainting
  • Lethargy
  • Exercise intolerance
  • Abdominal extension
  • Grey or blue gums

If your dog is displaying any of these symptoms they need to seek medical attention immediately.

What Causes a Heart Murmur in Dogs

heartworm disease in dogs

The specifics of each type of heart murmur dictate the underlying cause. There are many types of heart defects and heart disease that can lead to heart murmurs. However, there are a few causes that are pretty universal as far as heart murmur causes.

In general, heart murmurs are caused by disturbances in blood flow that can be separated into three categories:

  • Blood disturbances caused by regurgitant flow caused by an incompetent valve, patent ductus arteriosus, or a defect in the septum. (The septum is the wall that separates the left and right side of the dog’s heart)
  • Blood disturbances caused by high flow through normal or abnormal valves or vibrations within the blood flow.
  • Blood disturbances caused by outflow obstruction, or forward flow through diseased valves or dilated vessels.

Heart murmurs can also be caused by:

  • Heart valve deficiencies
  • Blockage of the heart valve
  • Defects in the heart walls
  • A weakening of the heart muscle walls (known as dilated cardiomyopathy)
  • Heartworm disease
  • An infection of the heart valves (known as endocarditis)
  • Tumors

Again, these are the general causes of heart murmurs. In the next section, we’ll get into specifics.

Causes of a Systolic Murmur

The majority of heart murmurs are diagnosed as systolic.

The most common cause of systolic murmurs is when the blood vessel narrows and causes obstruction of the blood flow. This is also referred to as pulmonic stenosis or subaortic stenosis.

Additional causes of a systolic murmur include:

  • Anemia
  • Hyperthyroidism
  • Heartworm disease
  • Mitral and tricuspid valve heart failure
  • Cardiomyopathy and aortic valve insufficiency
  • Mitral and tricuspid valve dysplasia
  • Systolic anterior mitral motion (SAM)
  • Aortic valve insufficiency
  • Obstruction of the right ventricular outflow
  • Aortic stenosis
  • Atrial and ventricular septal defect
  • Inflammation of the inner part of the heart

Causes of a Diastolic Murmur

Diastolic murmurs in dogs are rare.

These murmurs are most commonly due to an aortic insufficiency. Aortic insufficiency occurs when the aortic valve leaks because it is not able to close tightly.

Additional causes of diastolic murmurs are:

  • Mitral and tricuspid valve stenosis
  • Aortic and pulmonic valve endocarditis (inflammation of the inner layer of the heart)

Causes of a Continuous Murmur (Also known as Machinery)

Continuous murmurs are most often associated with a congenital heart defect called patent ductus arteriosus (PDA).

Continuous murmurs can also be caused by:

  • Aortic stenosis with aortic regurgitation
  • A ventricular septal defect with aortic regurgitation

Structural Heart Problems

Four chambers compose the heart:

  • The left atrium
  • The left ventricle
  • The right atrium
  • The right ventricle

The blood flows from the right side of the heart, moves through the pulmonary artery, and to the lungs where it is oxygenated. Once oxygenated, the blood flows to the left side of the heart and to the aorta. It is then pumped through the rest of the body.

When a dog has structural heart disease, there is a disturbance in the blood flow that creates a turbulence. An abnormal structure or defect usually cause the disturbance.

The abnormality may be:

  • A thickening or narrowing of a valve
  • A thickening or narrowing of a large blood vessel
  • A leaky heart valve
  • A hole between the heart chambers
  • A hole between two arteries

Congenital Heart Structural Problems

If the structural heart problem is categorized as congenital, it means that the dog was born with the condition.

Some congenital heart diseases are hereditary in certain breeds. Veterinary cardiologists will find diseases such as sub-aortic stenosis, pulmonic stenosis, and patent ductus arteriosis much more prevalent in some dog breeds over others.

Murmurs Caused By Acquired Heart Structural Problems

An acquired heart problem develops later on in the dog’s life. The most common cause of an acquired structural heart problem is a condition known as mitral insufficiency (also referred to as mitral regurgitation).

Mitral insufficiency occurs when the mitral valve thickens and begins leaking. The condition is most common in small breed dogs mostly due to the fact that their valves are smaller and can become blocked more easily.

Acquired heart murmurs can also occur in older dogs. Most commonly the condition is caused by bacterial endocarditis or dilated cardiomyopathy.

Bacterial endocarditis is a bacterial infection that localizes on a heart valve.

Dilated cardiomyopathy (DCM) occurs when the left ventricle of the heart becomes enlarged and weakened, and its ability to pump blood is significantly decreased.

Murmurs Caused By Extracardiac Heart Problems

Extracardiac heart problems can cause a condition known as a functional heart murmur.

A functional heart murmur can be due to ailments such as:

  • Anemia (low level of red blood cells)
  • Hypoproteinemia (low protein levels in the blood)
  • Fever
  • Infection

When functional heart murmurs occur due to anemia or hypoproteinemia, the blood is too watery. As the thin blood flows through the valves it creates the turbulence that is indicative of a heart murmur.

Additionally, with young puppies conditions such as anemia and hypoproteinemia can be due to an infestation of parasites. With adult dogs, the conditions may be caused by blood loss or a severe underlying issue.

Additional conditions that may lead to a functional heart murmur are:

  • Pregnancy
  • Obesity
  • Emaciation

The causes of most extracardiac heart problems are preventable. It is important for pet owners to stay on top of their dog’s hygiene and keep up to date on vet visits.

What is an Innocent or Physiologic Heart Murmur

An innocent murmur or physiologic heart murmur is not serious and more often than not will resolve in time. The murmur will have no negative impact on the dog’s life.

Additionally, a physiologic or innocent heart murmur will be of low intensity, meaning a Grade III or less.

Innocent of physiological heart murmurs are benign.

What Causes an Innocent or Physiological Heart Murmur

Innocent heart murmurs are relatively common in puppies since they are growing so quickly. In general, a veterinary cardiologist may detect an innocent heart murmur when the puppy is around 6-8 weeks old. By 4-5 months, old the puppy has usually outgrown the murmur.

Heart Murmur – Not Always Dangerous

Heart murmurs are not considered to be normal. With that being said, they are not always a cause for alarm.

In puppies, heart murmurs may be more common than you might expect. In fact, it’s quite possible that your dog may have had a heart murmur as a puppy and has since grown out of it without you even realizing.

On the other hand, some heart murmurs are serious and treating them appropriately can be the difference of life or death. When the murmur doesn’t go away, your veterinary cardiologist will need to determine the underlying issue that is causing the heart murmur in order to develop an appropriate treatment method.

Diagnosing a Heart Murmur in Dogs

Diagnosing a heart murmur may require a number of tests.

Generally, a veterinary cardiologist will listen to the dog’s heart with a stethoscope. From what they hear, they will be able to determine the type of murmur that your dog has based on how loud it is and where it is coming from.

However, perhaps the most crucial information is the underlying cause of the heart murmur. Once the type and grade of the heart murmur are determined, additional testing such as radiographs, echocardiograms, ultrasounds, and an electrocardiogram may be required in order to pinpoint the cause.

A veterinarian will also consider information such as your dog’s age, breed, and weight when diagnosing the underlying cause of the heart murmur. Certain breeds are more common to develop murmurs as well as certain conditions such a heartworm disease can predispose a dog to heart issues.

Furthermore, it is important for pet owners to realize that in many cases of heart murmurs there are no clinical signs. Therefore, it is important to maintain regular vet visits as a diagnosis may only be possible during your yearly checkup.

What Does a Heart Murmur Sound Like

Your veterinarian will differentiate between a number of abnormal sounds in order to help diagnose what is causing the heart murmur.

Similarly to a human heart, the veterinarian will listen for a “lub” and “dub” sound. When a dog has a heart murmur the “lub-dub” sound is followed by a “whooshing” sound.

These sounds can be also described as:

  • Split sounds
  • Ejection sounds
  • Gallop rhythms
  • Clicks

What Does a Heart Murmur Feel Like

In high-grade heart murmurs, the dog owner will be able to feel heart vibrations through the chest wall solely by placing their hand on the dog’s chest.

Heart Murmur Treatment

heart murmur treatment for dogs

The course of treatment will vary based on the type of heart murmur that your dog is diagnosed with.

Also, it is important to note that you will not be treating the heart murmur itself, but rather the underlying cause of the murmur. This is why it is so important for the dog’s heart murmur to be accurately diagnosed.

In cases of physiological murmurs (innocent murmurs), treatment is not required. However, routine checkups will be necessary.

In the case of an underlying issue causing the murmur, the veterinarian may advise a combination of a specialized diet and medication. Again, this will be to treat whatever underlying issue is causing the murmur.

When the heart murmur is caused by a congenital heart defect, such pulmonic stenosis or patent ductus arteriosus, surgery may be recommended to correct it. Determining whether to have the surgery should be on a case-by-case basis as it’s not always the proper choice.

A heart murmur caused by an underlying condition such as heartworm disease may be able to resolve completely with the appropriate treatment plan.

Your dog will receive outpatient treatment unless heart failure is evident.

Prognosis for Dogs with Heart Murmurs

Again, the prognosis for dogs with heart murmurs really varies based on the murmur itself.

While it may sound cliche and impossible at the time, it is important for dog owners not to panic. The first step towards addressing the disease is detecting the heart murmur. Now a treatment plan can begin.

While some heart murmurs may never require much intervention, others will be a condition that the pet owner has to be aware of every day for the rest of their dog’s life.

Regardless of the type of murmur, ongoing monitoring is always necessary to ensure that additional issues do not form and the condition doesn’t get worse.

Preventing Heart Murmurs in Dogs

Some heart murmurs, like those that are congenital, are not preventable.

However, there are others, such as most extracardiac murmurs, that are due to parasite infections. These murmurs are preventable with proper hygiene care and monitoring the dog’s health. Pet owners should take any signs of physical abnormalities very seriously and have a veterinarian’s professional diagnosis.

Additionally, there are some murmurs that can develop from obesity. Making sure that your dog maintains a proper weight is a significant way to help prevent murmurs from forming.

Managing Heart Murmurs in Dogs

Treating and managing heart murmurs are critical responsibilities of pet owners. It is extremely important to stay on top of your dog’s medication and diet and know when something seems “off.”

While a heart murmur diagnosis can be scary, it is manageable with proper treatment.

Living with Heart Murmurs

dog living with heart murmur

Hearing that your veterinarian say the words heart murmur in dogs can be gut-wrenching. Knowing that there is something wrong with such a vital organ causes an unimaginably overwhelming for a pet owner.

However, this is not the end of the road for your beloved pup. Understanding the diagnosis and determining a treatment plan are paramount and make a world of a difference for both you and your dog.

Ask questions, stay informed, and be sure to monitor your dog’s day-to-day life. Living a full, happy life with a heart murmur is absolutely possible.


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About the author

Chelsea Hunt-Rivera

Chelsea Rivera is a Dedicated Pet Parent who loves to create amazing content for pet owners and is helping change pet wellness as the Head of Content for Honestpaws.com.