Mastiff Health
Heart Murmur in Dogs1
By Anna Burke
You don’t need to be a doctor to know that hearts are important, and so it is understandable to be concerned if your veterinarian diagnoses your dog with a heart murmur.
Before you panic, however, there are a few things you need to know.
First of all, there are several different types of heart murmurs. Some are more serious than others, and many heart murmurs, and the underlying conditions that cause them, are treatable.
Here are the basics to help you wrap your head around heart murmurs, and remember that you can always ask your veterinarian for clarification about your dog’s condition.
What Is a Heart Murmur?
Dog’s hearts, like ours, pump blood through their bodies. You've probably listened to your own heartbeat or a loved one's at some point in your life, and so you know that hearts beat regularly as they pump the blood that keeps us alive.
When there is a disturbance in this blood flow, it creates an audible noise, called a murmur, that is distinguishable from a regular heartbeat with a stethoscope.
Veterinarians break murmurs down into several different classifications. The most important classifications for you to know are the type and configuration (or quality).
Types of Heart Murmurs
There are three types of murmurs: systolic, diastolic, and continuous. This classification is based on the timing of the murmur. Systolic murmurs, for instance, are murmurs that take place when the heart muscle contracts, whereas diastolic murmurs happen when the heart muscle is relaxed in between beats. Continuous murmurs, on the other hand, happen throughout your dog’s regular heartbeat cycle.
Knowing the type of murmur can help your veterinarian figure out what is causing the murmur.
Heart Murmur Grade
Another tool veterinarians use to help diagnose the cause of the murmur is grading. Heart murmurs in dogs are graded on a scale of one to six.
- Grade I murmurs are the least serious and are barely detectable with a stethoscope.
- Grade II murmurs are soft, but your veterinarian can hear them with the help of a stethoscope.
- Grade III murmurs have a loudness that falls in the middle of grades II and IV. Most murmurs that cause serious problems are at least a grade III.
- Grade IV murmurs are loud and can be heard on either side of the chest.
- Grade V murmurs are very loud and can be heard with a stethoscope without difficulty, and can also be felt by holding a hand against the dog’s chest.
- Grade VI murmurs, like grade V murmurs, are very loud and can be felt through the chest wall, and are the most severe of the heart murmurs.
As your doctor listens to your dog’s heart murmur, you may also hear her talk about the configuration of the heart murmur. This describes the way the heart murmur sounds.
Heart Murmur Configurations
There are four main types of configurations (sometimes referred to as qualities): plateau, crescendo-decrescendo, decrescendo, and machinery.
- Plateau murmurs are characterized by a uniform loudness. These murmurs are usually associated with an aortic valve insufficiency.
- Crescendo-decrescendo murmurs, like their name implies, get louder and then quieter. These are associated with conditions such as aortic and pulmonic stenosis.
- Decrescendo murmurs start off loud and then grow quieter. These murmurs are commonly seen with aortic valve insufficiency or a ventricular septal defect.
- Machinery quality, or continuous murmurs, are associated with patent ductus arteriosus (PDA), which is a congenital heart defect.
What Causes Heart Murmurs in Dogs?
Once your veterinarian has explained what kind of murmur your dog has, and its grade of intensity, your next question will probably be “what is causing my dog’s heart murmur?”
There are many different types of heart diseases and defects that can lead to heart murmurs. Figuring out the cause is something your veterinarian will attempt to do based on your dog’s age, breed, and test results.
In general, the causes of heart murmurs in dogs can be broken down into a few categories of blood flow disturbances.
- Disturbances caused by abnormal valves or vibrations
- Disturbances caused by obstruction, diseased valves, or dilated vessels
- Disturbances caused by regurgitant flow
Causes of Systolic Murmurs in Dogs
Most heart murmurs are systolic. The most common cause of systolic murmurs is pulmonic stenosis or subaortic stenosis, which is a narrowing of the blood vessel that causes obstruction of the blood flow. Other conditions that can cause systolic murmurs include:
- Anemia
- Heartworm disease
- Hyperthyroidism
- Cardiomyopathy
- Aortic valve insufficiency
- Mitral and tricuspid heart failure
- Systolic anterior mitral motion (SAM)
- Endocarditis of the mitral and tricuspid valve
Causes of Diastolic Murmurs in Dogs
Diastolic heart murmurs are rare in dogs. The most common condition associated with diastolic murmurs is aortic insufficiency, which is when the aortic valve does not close tightly, and therefore leaks. Mitral and tricuspid valve stenosis, and aortic and pulmonic valve endocarditis can also cause diastolic murmurs.
Causes of Continuous Murmurs in Dogs
Continuous murmurs are most commonly caused by PDA, but aortic regurgitation caused by a ventricular septal defect, and aortic stenosis with aortic regurgitation, can also cause a continuous murmur.
Innocent Murmurs in Dogs
Heart murmurs sound serious, and often are, but sometimes a heart murmur is classified as an innocent heart murmur. These heart murmurs are not serious and often resolve with time. They are most commonly found in young dogs and are typically a grade III or less.
How Are Heart Murmurs Diagnosed?
Heart murmurs are typically diagnosed with a stethoscope. Your veterinarian will listen to your dog’s heart, and based on what he or she hears, how loud it is, and where it is coming from, will determine the type of heart murmur your dog has.
Once the type and grade of heart murmur are identified, your veterinarian will then proceed to try to diagnose the cause.
One of the ways your veterinarian narrows down a potential cause is based on your dog’s overall health, age, and breed. Certain conditions, for example heartworm disease, can predispose a dog to heart problems, and certain breeds of dogs are prone to certain heart diseases or abnormalities. Young dogs can present with an innocent murmur that resolves with age, but older dogs with heart murmurs typically have an underlying condition that requires medical attention.
Diagnosing the underlying condition may require additional testing. Radiographs, echocardiograms, and an electrocardiogram can help your veterinarian diagnose the underlying cause, and she may suggest additional tests based on her suspicions.
How Are Heart Murmurs Treated?
It's important to note that you don't treat heart murmurs. You treat symptoms and problems associated with heart murmurs. Since heart murmurs are usually the result of an underlying condition, the treatment for your dog’s heart condition will depend on the diagnosis. For example, the treatment for heartworm or hyperthyroidism is drastically different from the treatment for congestive heart failure. In some cases, especially with young dogs with mild murmurs, the murmur may even resolve on its own.
What Is the Prognosis for a Dog With a Heart Murmur?
Heart murmurs can be serious, but they are not a cause for panic. Many of the causes of heart murmurs are treatable, and in some cases, may resolve on their own. In more serious cases, however, especially with older dogs, the prognosis may be more guarded, but just remember that catching a heart murmur is the first step toward addressing the disease.
Heart murmurs can be complicated to wrap your head around. There are many possible causes, and distinguishing between the types and grades gets confusing, especially if you don’t have a medical background. If you have further questions about heart murmurs in dogs, consult your veterinarian, and don’t be afraid to ask her to point you in the direction of client handouts and materials that will provide more information about your dog’s condition. She might advise you to consult a veterinary cardiologist, usually available at most veterinary specialty services.
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Updated: 2/21/2023