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Heart Murmurs in Dogs

Your dog's heart works very hard to keep their blood flowing, carrying vital oxygen throughout their body. But sometimes, an issue can arise that impacts the function of their heart. Here, our Nashua veterinary specialists discuss the causes, signs, and treatment of heart murmurs in dogs.

What is a heart murmur in dogs?

Murmurs are additional heartbeats that occur because of a disturbance in the blood flow that is strong enough to be found with an auditory diagnosis (i.e., listening). Various characteristics are often used to classify heart murmurs. For example, systolic murmurs happen during the heart muscle's contraction. In contrast, diastolic murmurs occur during the moments the heart muscle relaxes between pumps, and continuous/to-and-fro murmurs happen during almost all of the heartbeat's process.

What are the symptoms of heart murmurs in dogs?

Heart murmurs in dogs have various symptoms, which depend on their location, grade, and configuration. However, if the murmur is associated with structural heart disease, your dog might exhibit signs of congestive heart failure, such as coughing, weakness, or exercise intolerance.

Some common symptoms of heart diseases and disorders include:

  • Lack of energy or appetite
  • Irregular heartbeat or racing pulse
  • Gums and/or tongue are bluish
  • Excessive panting, even when resting
  • Hacking, persistent cough
  • Severe water retention
  • Collapsing or fainting

What are the causes of heart murmurs in dogs?

A wide range of conditions and diseases can cause a heart murmur in dogs.

Most commonly, heart murmurs in small dogs are caused by a leaky mitral valve (the heart valve 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 blood to flow back into the left atrium. When it comes to heart murmurs in older dogs, what happens is that the valve degenerates, which causes blood to leak backward. This condition is also known as chronic valve disease, degenerative mitral valve disease, or endocardiosis.

In larger breed dogs, heart murmurs are often caused by a disease called dilated cardiomyopathy (with a subsequent leaky mitral valve). Dilated cardiomyopathy weakens the muscles in the heart's pumping chamber and decreases the heart's contraction strength.

Specific illnesses and conditions, such as the following, can also cause heart murmurs:

Systolic Heart Murmurs

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

Continuous or To-and-Fro Heart Murmurs

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

Diastolic Heart Murmurs

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

How are heart murmurs diagnosed?

Your veterinarian can distinguish between a wide range of abnormal heart sounds, including split sounds, gallop rhythms, clicks, and ejection sounds. They must also differentiate between abnormal heart and lung sounds and identify any relationship between the timing of the sound and either breathing or heartbeat.

Your vet might also recommend additional diagnostic testing such as X-rays of your dog's chest, complete blood count, and echocardiography.

Heart Murmur Grades in Dogs

Grade I (1) Heart Murmur in Dogs: So quiet it can hardly be heard
Grade II (2) Heart Murmur in Dogs: Quiet, but can be heard with a stethoscope
Grade III (3) Heart Murmur in Dogs: Medium-loud, usually related to mechanical blood circulation problems
Grade IV (4) Heart Murmur in Dogs: Loud, able to 'echo' widely, including both sides of the chest
Grade V (5) Heart Murmur in Dogs: Very loud, a vet can hear it with a stethoscope barely touching the chest; it can also be physically felt through the dog's chest
Grade VI (6) Heart Murmur in Dogs: Very loud, the murmur is audible with a stethoscope barely on the dog's chest; the vibration is strong enough to be felt through the chest

How are heart murmurs in dogs treated?

Thankfully, unless your dog is or has a chance of going into heart failure, its condition is most likely treatable on an outpatient basis. However, 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.

A heart murmur caused by cardiac disease or defect may require medication, a specialized diet, or surgery. At the very minimum, your dog will require vet visits every six months to monitor the murmur. Depending on your dog's condition, this visit may require a repeat echogram and/or X-rays.

Your veterinarian or specialist will develop and explain to you the best possible treatment and monitoring plan for your pup's condition.

Is a heart murmur fatal in dogs?

For dogs diagnosed with a heart murmur, their life expectancy largely depends on the underlying cause and ranges from good to severe. The prognosis is generally good to excellent for innocent murmurs that don't require treatment. 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.

The prognosis for dogs with congenital heart defects varies, but if the defect can be corrected by surgery, it 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.

Is your dog experiencing symptoms indicating a heart issue? Ask your vet for a referral to our cardiology departmentContact us today to learn more about our services.

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Animal Medical Center of New England welcomes emergency walk-ins and appointments when your pet needs us most. Our team of specialists is also accepting referrals from primary care veterinarians - fill out a referral form to get started.


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