Ask the NorthStar VETS Vet: Heart Murmurs in Dogs and Cats


My pet has a heart murmur – what does this mean?

A heart murmur is one of several types of abnormal sounds your veterinarian can hear when listening to your pet’s heart with a stethoscope. Normally, two distinct sounds are heard when listening to the heart of a normal dog or cat. These are often described as “lub” and “dub.” When listening with a stethoscope one hears: Lub-dub…Lub-dub….Lub-dub.

A murmur is an abnormal extra sound (which can sometimes drown out the normal sounds). Murmurs most commonly occur between the “lub” and the “dub” and have a “shooshing” or “whooshing” quality.

Hearing a heart murmur during a routine physical examination will often be the first hint to your veterinarian that your pet has heart disease. Hearing a murmur is only a hint that something may be wrong (a clinical sign), not a final diagnosis. Hearing a murmur is reason to consider more discussion and tests to determine the cause of the murmur (the diagnosis). Knowing the diagnosis and severity of the cause of the murmur allows your veterinarian (or a cardiologist they consult) to provide you with an educated guess (prognosis) regarding how this heart problem may affect your pet in the future.

Hearing a murmur is not a reason to panic. Many dogs and cats with murmurs live normal lives and never need any treatment for heart disease. But the only way to know for certain is to work with your veterinarian to determine the cause and severity of the cause of the murmur.

What causes a heart murmur?

The short answer to this question is “turbulent blood flow.” Like the water in a calm river or stream, blood flowing normally flows through the heart with laminar flow – that is, it is smooth and undisturbed. And like a river or stream, narrowing, or other causes of more rapid flow, will disrupt this smooth laminar flow. In a river the turbulent rapids emit sounds much louder and less tranquil than the calmer sections of river. In the heart we hear this turbulence as a murmur.

Murmurs caused by abnormalities of the heart can be due to:

  • Valvular diseases
  • A narrowing (stenosis) within a chamber or vessel through which the blood has to “squeeze” through, like water through a pinched hose
  • A “hole in the heart” between two chambers or two arteries that are not normally connected
  • A thicker than normal heart muscle

What is a benign or “innocent” murmur?

Some heart murmurs are called benign (or innocent or physiological), meaning there is no apparent heart disease that explains the murmur. These murmurs are often seen in puppies, and can occur in cats of any age. They are uncommon in adult dogs. Benign murmurs are usually soft (rather than loud), and can be intermittent. Benign puppy murmurs will generally disappear by 12 to 15 weeks of age. Murmurs associated with anemia or excitement are also considered benign murmurs.

What is a congenital murmur vs. an acquired murmur?

A congenital murmur is a murmur in a pet that is present from birth (or near birth). Congenital murmurs are associated with heart defects that the pet was born with. However, some congenital murmurs may be missed in puppies or kittens and only detected later in life. An acquired murmur is a murmur that a pet acquires during their life. These can be benign, but more often (especially in dogs) are associated with developing heart or valve disease.

My pet’s murmur has a “grade.” What does this mean?

Murmur grading is simply your veterinarian’s way of describing the loudness of a murmur. There are six murmur grades. The lower the grade, the quieter the murmur. However, it is often easiest to simply describe them as “soft,” “moderate,” or “loud.” There are other terms that a vet will use to describe the character of a murmur – this helps communicate to other veterinarians the characteristics of the murmur as certain types of murmurs are more commonly associated with specific heart or valve diseases.

The grade or loudness of the murmur is only sometimes related to the severity of the heart abnormality causing it. Bear in mind that grading is subjective because it is based on how it sounds to the listener. Also, it’s hard to tell if an animal has a heart murmur if the pet is excited or anxious, because rapid breathing sounds can mimic a murmur. Usually, only a trained cardiologist can identify a Grade 1 murmur. A Grade 5 or Grade 6 murmur is so strong that it can be felt through the chest wall (like water being sprayed against a sheet of cloth).

Echocardiograms at NorthStar VETS

What should I do if my pet has a murmur?

In many cases, a veterinarian will be able to determine the likely cause of a murmur in a dog just by listening. In some cases, no additional testing will be deemed necessary. However, to be certain, it is often best to work with your veterinarian to confirm the cause of the murmur as well as the severity of the condition that is causing the murmur. This will give you the best idea of what to expect in the future — the prognosis for your pet. In other cases, where a pet may be used for breeding, a murmur may indicate the presence of a hereditary defect that could be passed on to progeny.

The cause of a cat’s murmur cannot usually be determined by listening alone. In many cats, benign murmurs can sound exactly like murmurs in a cat with serious heart disease.

In both dogs and cats, your veterinarian may elect to perform chest radiographs (x-rays), an echocardiogram (ultrasound of the heart), or other imaging studies, or to refer your pet to a specialist for these procedures. The tests that are performed depend on the individual case.

How is a murmur treated?

The murmur itself is not treated. The underlying cause of the murmur may or may not be treated – this depends on the cause, severity, and other circumstances (age, well-being of the pet, cost of treatment etc). Your veterinarian is best-suited to discuss specific treatment options with you.

If your pet needs to see a veterinary Cardiologist in our Cardiology service, call NorthStar VETS at 609.259.8300. Once your appointment is set, you may complete your Cardiology pre-appointment paperwork.

Jennifer Schneiderman, DVM, DACVIM (Cardiology)Jennifer Schneiderman, DVM, DACVIM (Cardiology)
Dr. Schneiderman received her Doctorate of Veterinary Medicine degree at Ross University in 2009 before moving back home to Long Island, New York where she completed a one-year rotating internship in small animal medicine and surgery at Atlantic Coast Veterinary Specialists in March 2010. After that, she completed a three-year residency in Cardiology at Atlantic Coast Veterinary Specialists in July 2013 and then stayed on there as a Staff Cardiologist until June 2014. Now a board-certified Veterinary Cardiologist, Dr. Schneiderman joined the NorthStar VETS team in August 2014. Her clinical interests include treatment of congestive heart failure and complex arrhythmias along with an interest in interventional procedures such as pacemaker implantation, balloon valvuloplasty and patent ductus arteriosus occlusion. Outside of work, Dr. Schneiderman enjoys traveling, scuba diving, going to the beach and spending time with her two tuxedo cats.

The information presented on this web site is not intended to take the place of your family veterinarian’s advice and is not intended to diagnose, treat, cure or prevent any disease. Discuss this information with your own veterinarian to determine what is right for your pet. All information is intended for your general knowledge only and is not a substitute for medical advice or treatment for specific medical conditions. We can not and do not give you medical advice via this blog. The information contained in this online site and emails is presented in summary form only and intended to provide broad understanding and knowledge. The information should not be considered complete and should not be used in place of a visit, call, consultation or advice of your veterinarian. We do not recommend the self-management of your pet’s health problems.

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