What is a heart murmur?
A heart murmur occurs when there is turbulent blood flow within the heart. Some murmurs, especially those found in young puppies, can be 'innocent' or 'physiologic' and will not negatively affect your dog's health. Young puppies with innocent heart murmurs usually outgrow them by about 5 months.
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).
What are heart murmur grades in dogs?
Not all heart murmurs sound the same. When your vet listens to your dog's heart, they will assess the intensity, timing, and location of the murmur and grade it using the following scale:
Grade 1: Barely audible - the least serious type of heart murmur
Grade 2: Soft murmur, but easily heard with a stethoscope
Grade 3: Intermediate loudness, most serious problems will result in at least a grade 3 heart murmur in dogs
Grade 4: Loud murmur that can be heard on either side of the chest
Grade 5: Very loud murmur
Grade 6: Very loud murmur that can be felt by placing a hand on the dog's chest wall - the most severe type of heart murmur
What are the symptoms of heart murmurs in dogs?
The symptoms of a heart murmur largely depend on the underlying heart condition that is affecting your pup. Some common symptoms of heart diseases and disorders include:
- Irregular heartbeat or racing pulse
- Hacking, persistent cough
- Excessive panting even when resting
- Lack of energy or appetite
- Collapsing or fainting
- Gums and/or tongue are bluish
- Severe water retention
What conditions cause heart murmurs in dogs?
There is a wide range of conditions and diseases that can cause a heart murmur in dogs.
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 endocardiosis.
In larger breed dogs, heart murmurs are often caused by a disease called dilated cardiomyopathy (with a subsequent leaky mitral valve). Dilated cardiomyopathy is a disease that causes the muscles in the pumping chamber of the heart to become weakened and decrease the contraction strength of the heart.
While these are common culprits of heart murmurs, there is a range of other issues that can cause a murmur to occur. Your vet will be able to run the proper diagnostic tests to properly assess your pet's heart and determine the cause of the heart murmur.
How can heart murmurs be treated?
Treatment for your dog’s heart murmur will depend on the underlying cause. An innocent murmur will not require any treatment, but your vet will want you to come for follow-up appointments to ensure the heart murmur resolves itself.
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 6 months to monitor the murmur. This visit may require a repeat echogram and/or X-rays depending on your dog's condition.
Your primary veterinarian will advise you on the best course to treat and monitor your dog’s heart murmur. In some cases, this may include a referral to a veterinary cardiologist for specialized cardiology care.
What is the prognosis of a heart murmur?
The prognosis of 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.
For dogs that have a leaky mitral valve, long-term medication can help prolong their lives or improve their quality of life. The prognosis for a dog with dilated cardiomyopathy varies - if the dog is already showing signs of heart failure the prognosis is unfortunately not good.
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.