Heart Murmur in Dogs

Written by Small Door's medical experts

A dog’s heart functions in the same way as their human owner’s heart — they too can experience similar heart problems and conditions. A veterinarian can detect a heart murmur during routine checkups, and most owners are usually unaware their dog has one.

In This Article

What is a heart murmur in dogs?

A heart murmur is an abnormal heart sound caused by a disturbance in the blood flow. It can be heard when using a stethoscope to listen to a dog's heart. There are several types of heart murmurs, some more serious than others. Depending on the underlying conditions that result in a murmur, they may be treatable.

What’s important to remember is that a heart murmur is a symptom and not a disease, and while it can be indicative of an underlying heart problem, it can also be completely innocent.

Signs and symptoms of heart murmur in dogs

A heart murmur is an extra heart vibration which results in an abnormal sound caused when there is a disturbance in the blood flow. The detectable noise is one that is distinguishable from a regular heartbeat and can be heard by a doctor with the use of a stethoscope.

If your dog has a murmur, it is not an immediate cause for panic. Talk with your vet about heart disease and what it might mean for your dog should there be something more serious going on. Many dogs diagnosed with heart murmurs never need any treatment and go on to live long and healthy lives. Symptoms include:

  • Irregular heartbeat

  • Hacking, persistent cough

  • Excessive panting even when resting

  • Tires easily

  • Lack of energy

  • Collapses or faints

  • Gums and/or tongue are bluish in color

  • Racing pulse

  • Lack of appetite

  • Severe water retention

These symptoms may also be indicative of a more serious health risk and not necessarily a heart murmur. Your veterinarian will be able to determine exactly what’s going on if your dog is exhibiting any of these signs.

What causes a heart murmur in Dogs?

The cause of a heart murmur varies. Some murmurs are determined to be “innocent” or “physiologic,” while other times, they are determined to be pathologic or caused by a disease, such as a structural problem within the heart (cardiac disease). Murmurs can also be due to a problem that is “extra-cardiac,” meaning they are not caused by heart disease.

What structural heart problems cause a heart murmur?

Structural heart problems arise when there is an abnormal defect or structure that is causing blood flow issues in the dog's heart. When the blood flow is disrupted it creates turbulence. Some examples of heart abnormalities that cause turbulence include leaky heart valves, large blood vessels, an unusual hole between two arteries or heart chambers that should not be connected, and narrowing or thickening of a heart valve. If a dog is born with structural heart problems, it is called a congenital heart problem. If the dog develops a structural heart problem later in life, it’s called an acquired heart problem. Both congenital and acquired structural heart problems are able to cause heart murmurs in dogs.

What extra-cardiac problems cause a heart murmur?

Extra-cardiac problems will cause a functional heart murmur. A functional heart murmur is a heart murmur that is caused by physiological conditions outside of the heart. These physiological conditions include fever or infection, pregnancy, emaciation, obesity, anemia, and hypoproteinemia.

Anemia and hypoproteinemia cause a dog's blood to become too watery and results in turbulence within the blood flow. Adult dogs typically become anemic due to issues such as blood loss or severe disorders. In puppies, anemia and hypoproteinemia can be caused by an extreme infestation of parasites, worms, fleas, and ticks which can become fatal if not treated.

Do all heart murmurs sound the same?

No, heart murmurs in dogs can vary by volume, the time in which they occur during the heart cycle, location, and the length of time the murmur can be heard. We will explain all of these and what they mean in-depth in the sections below.

Types of heart murmurs in dogs

Heart murmurs can be broken down into three types: systolic, diastolic, and continuous.

Systolic murmur: Most heart murmurs are systolic and occur during systole, the phase of the heart cycle when the heart contracts to pump blood out. The most common cause of this murmur is a leaky mitral valve (the valve between the left upper and lower chambers of the heart). Pulmonic stenosis or subaortic stenosis, which is a narrowing of the blood vessel that obstructs the blood flow, are less common causes of systolic murmurs.

Diastolic murmur: This type of murmur is uncommon in dogs. The most common condition associated with this type of murmur is aortic insufficiency, which occurs when the aortic valve leaks as a result of the fact that it does not close tightly.

Continuous murmur: This type of murmur is most often caused by patent ductus arteriosus (PDA), which is a failure of a large blood vessel, the ductus arteriosus, to close just after birth. It is the most frequent congenital defect in dogs. The breeds most commonly affected are Maltese, Pomeranian, Poodle, Keeshond, Bichon Frise, Chihuahua, and German Shepherd.

Grades of heart murmurs in dogs

Heart murmurs are also graded on a scale of 1 to 6, with 1 being the softest and hardest to hear, and 6 being the loudest. Veterinarians go by the number scale to determine the cause of the murmur and the best course of action to take, if necessary.

  • Grade 1 – These are the least serious. They are extremely soft in sound and barely audible.

  • Grade 2 – A soft sound heard through the use of a stethoscope.

  • Grade 3 – Intermediate loudness and radiates to more than one location.

  • Grade 4 – These murmurs are moderate to intense and can be heard on each side of the chest.

  • Grade 5 – Very loud and can be heard even when the stethoscope is barely touching the chest. They can also be felt by holding a hand against the chest.

  • Grade 6 – Like a grade 5, these murmurs are very loud and can be felt by touching the chest; they are also the most severe.

Heart murmur configurations in dogs

Heart murmurs in dogs have four main configurations or qualities which are plateau, crescendo-decrescendo, decrescendo, and machinery.

  • Plateau murmurs: This type of murmur is normally connected with an aortic valve insufficiency and creates a constant loudness.

  • Crescendo-decrescendo murmurs: This type of murmur is normally connected with aortic and pulmonic stenosis or similar conditions and creates a noise that changes back and forth from louder to quieter.

  • Decrescendo murmurs: This type of murmur is normally connected with a ventricular septal defect or aortic valve insufficiency and starts off loud then becomes quieter. 

  • Machinery murmurs: This type of murmur is connected with patent ductus arteriosus and is a continuous murmur.

It’s best to consult with your veterinarian to learn more about the specific heart murmur that your dog has so you can best do further research on the correct configuration.

What is an innocent or physiologic heart murmur?

Not every murmur is an indication of a heart disorder. An “innocent” or “physiologic” murmur means that the murmur does not have an impact on the dog’s health. These types of murmurs are commonly seen in young puppies, especially larger breeds, as they begin to grow rather quickly. A puppy with an innocent heart murmur will most likely outgrow it by around four to five months of age.

Diagnosing a heart murmur in dogs

A veterinarian detects heart murmurs with a stethoscope by listening to the sound and how loud the murmur is and where it’s coming from. The type and grade of the murmur will help determine the cause; age, breed, and health are also taken into consideration. There are also different tests such as chest X-rays, echocardiogram, electrocardiogram, blood and urine tests to get to the underlying cause of the murmur. Once the root issue is uncovered, a course of treatment can be determined.

Treatment for heart murmur in dogs

When it comes to the treatment of a heart murmur, a veterinarian will look to treat the underlying cause and the symptoms associated with it. Medical treatment may include a change in diet, exercise restrictions, and medication. In the case of young puppies and murmurs, they may often resolve on their own.

Is there a cure for a heart murmur in dogs?

There is no specific cure for a heart murmur, as they are the result of an underlying problem. The root cause needs to be determined and addressed to treat the murmur.

Is a heart murmur contagious for humans and other pets?

Dogs diagnosed with heart murmurs should not be bred due to the risk of worsening their heart disease during the stress of breeding or pregnancy as well as the possibility of passing on the heart disease to their babies.

What is the cost of treating a heart murmur in dogs?

The cost of treatment varies greatly depending on the cause of the murmur and the dog’s age. Some cases will require surgery, and others may only need a modification in diet and medication. Your veterinarian will order specific tests to determine the condition accurately. Different factors such as who will perform the tests (i.e. your veterinarian or a specialist) as well as the area in which you live all can affect cost.

A breakdown of some of the tests and their expected costs:

  • Electrocardiogram – average cost is between $250 to $350

  • Ultrasound – $250 to $500

  • Chest X-rays – depending on the dog’s size, how many are needed, and
    whether a mild sedative is needed, can factor into the cost. Prices can
    range between $50 to $350.

The amounts are just an average estimate; combine them with the veterinary exam and you could be looking at upward of $1,500 to diagnose the condition.

Recovery and management of heart murmurs in dogs

A heart murmur is associated with an underlying condition. Many of those causes are treatable, and in some cases, the murmur may resolve on its own. The important thing is to catch it early and begin addressing the disease as soon as possible. Because a heart murmur is not necessarily a condition, the outlook varies based on treatment. Frequent checkups are required to monitor how well a dog is responding to treatment and ensure the murmur has not changed or gotten stronger.

Preventing heart murmurs in dogs

A heart murmur is a clinical finding that can’t be prevented in the normal sense of the word. The underlying cause for the murmur must be determined for a resolution to be possible. The murmur itself is not preventable or treatable, it is only a sound a veterinarian detects when listening to a dog’s heart.

Is there a vaccine for heart murmurs in dogs?

No vaccines are available.

Summary of heart murmurs in dogs

Heart murmurs can vary in their intensity and type. While they are usually caused by an underlying condition or heart disorder, some heart murmurs can be completely “innocent” and owners may even be unaware their dog has one. If you suspect your dog may have a heart murmur, it’s best to get it checked by a veterinarian to determine the severity and treat the underlying cause.

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