Heart Murmurs In Dogs

What does it mean if your dog is diagnosed with a heart murmur? Today, our Boulder specialist vet team tells you more about heart murmurs in dogs, including causes, types, and treatment.

What Are Heart Murmurs?

Murmurs are additional heartbeats that occur due to a disturbance in the blood flow that is strong enough to be detected with auditory diagnoses (i.e. listening). Heart murmurs are often classified according to a number of characteristics - for example, systolic murmurs happen during the heart muscle's contraction, diastolic murmurs occur during the moments the heart muscle relaxes between pumps, and continuous/to-and-fro murmurs happen during most of all of the heartbeat process. 

Symptoms and Types of Heart Murmurs in Dogs

The symptoms associated with murmurs depend on a variety of characteristics, including their grade, configuration, and location. If, however, the murmur is associated with structural heart disease, your dog may display signs 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 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)

How Are Heart Murmurs Diagnosed in Dogs?

Your vet is experienced in being able to tell the difference between a large number of abnormal heart sounds including split sounds, gallop rhythms, clicks, and ejection sounds. In addition, they must be able to differentiate between abnormal heart and lung sounds and identify any relationship between the timing of the sound and either 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. 

Grading Scale for Heart Murmurs in Dogs

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

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 your primary veterinarian diagnoses your dog with a heart murmur, contact us for a referral. Our talented Boulder veterinary cardiologists can provide your canine companion with the very best care.