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Heart Murmur in Dogs

What does it mean if your dog's heart murmur is diagnosed? Our Corpus Christi specialist vet team explains heart murmurs in dogs today, including their causes, types, and treatment options.

What is a Heart Murmur in Dogs?

Murmurs are extra heartbeats caused by a blood flow disturbance that is strong enough to be detected with auditory diagnoses (i.e. listening). Systolic murmurs occur during the contraction of the heart muscle, diastolic murmurs occur during the relaxation of the heart muscle between pumps, and continuous/to-and-fro murmurs occur during the majority of the heartbeat process.

Unfortunately, a heart murmur in an older dog is less likely to be deemed 'innocent' and can typically be categorized in two ways: pathologic (caused by heart disease) or extracardiac (not caused by heart disease). 

Symptoms and Types of Heart Murmurs in Dogs

Murmur symptoms are determined by a number of factors, including the grade, configuration, and location of the murmur. If the murmur is caused by structural heart disease, your dog may exhibit symptoms of congestive heart failure, such as coughing, weakness, or exercise intolerance.

What Causes Heart Murmurs in Dogs?

Heart murmurs in dogs can be caused by some of the following issues:

  • Blood flow disturbance related to high flow/unusual structural vibrations
  • Blood flow disturbance related to obstruction or diseased valves
  • Blood flow disturbance is related to backflow due to a compromised or dysfunctional valve, patent ductus arteriosus, or a defect in the heart's wall.

Heart murmurs can be caused by specific illnesses and conditions, including the following: 

Systolic Heart Murmurs

  • Anemia
  • Hyperthyroidism
  • Heartworm disease
  • Mitral and tricuspid valve heart failure
  • Cardiomyopathy and aortic valve deficiency
  • Mitral and tricuspid valve dysplasia
  • Systolic anterior mitral motion (SAM)
  • Dynamic right ventricular outflow obstruction
  • Dynamic subaortic stenosis
  • Aortic stenosis
  • Pulmonic stenosis
  • Atrial and ventricular septal defect
  • Tetralogy of Fallot
  • Mitral and tricuspid valve endocarditis (inflammation of the inner heart)

Continuous or To-and-Fro Heart Murmurs

  • Patent ductus arteriosus
  • Ventricular septal defect with aortic regurgitation
  • Aortic stenosis with aortic regurgitation

Diastolic Heart Murmurs

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

Most commonly, heart murmurs in small dogs are caused by a leaky mitral valve (the heart valve in between the left atrium and left ventricle). The mitral valve allows blood to flow from the left atrium to the left ventricle but does not allow for blood to flow back into the left atrium. Sometimes as a dog ages the valve degenerates which causes blood to leak backward. This condition is known as chronic valve disease, degenerative mitral valve disease, or endocarditis. 

How Are Heart Murmurs Diagnosed in Dogs?

Your veterinarian is trained to distinguish between a variety of abnormal heart sounds, such as split sounds, gallop rhythms, clicks, and ejection sounds. They must also be able to distinguish between abnormal heart and lung sounds and recognize any relationship between the sound's timing and breathing or heartbeat.

Additional diagnostic testing like X-rays of your dog's chest, complete blood count, and echocardiography may also be recommended by your vet. 

Heart Murmur Grades in Dogs

Grade I Heart Murmur in Dogs: So quiet one can hardly hear it.
Grade II Heart Murmur in Dogs: Quiet, but can be heard with a stethoscope
Grade III Heart Murmur in Dogs: Medium-loud, usually related to mechanical blood circulation issues 
Grade IV Heart Murmur in Dogs: Loud, able to 'echo' widely, including both sides of the chest
Grade V Heart Murmur in Dogs: Very loud, the vet can hear with a stethoscope barely touching the chest; can also be physically felt through the dog's chest
Grade VI Heart Murmur in Dogs: Very loud, the murmur is audible with a stethoscope barely on the dog's chest; vibration is strong enough to be felt through the chest 

How Are Heart Murmurs In Dogs Treated?

The good news is that unless your dog is or has a likelihood of going into heart failure, their condition can likely be treated on an outpatient basis. Although some dogs (e.g. puppies with a low-grade heart murmur) need little to no treatment, it is recommended to monitor the dog's health on an ongoing basis with routine diagnostic imaging

Is a Heart Murmur Fatal in Dogs?

The life expectancy of a dog with a heart murmur largely depends on the underlying cause of the murmur and ranges from good to severe. For innocent murmurs that don't require treatment, the prognosis is generally good to excellent. Heart murmurs caused by extracardiac disease or a functional problem that can be treated may resolve over time. 

Long-term medication for dogs with a leaking mitral valve can help prolong their lives or improve their quality of life. The prognosis for a dog with dilated cardiomyopathy varies; unfortunately, if the dog is already showing signs of heart failure, the prognosis is poor.

For dogs with congenital heart defects, the prognosis varies- if the defect can be corrected by surgery the prognosis is usually very good.

Note: The advice provided in this post is intended for informational purposes and does not constitute medical advice regarding pets. For an accurate diagnosis of your pet's condition, please make an appointment with your vet.

If you suspect something is wrong with your dog, contact Everhart Animal Hospital. Our advanced veterinary lab can detect and diagnose a wide variety of ailments.

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Everhart Animal Hospital is accepting new patients! Our experienced vets are passionate about the health of Corpus Christi companion animals. Get in touch today to book your pet's first appointment.

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