Heart murmurs in puppies

As part of a standard veterinary examination, your veterinarian will listen carefully to your dog’s chest with a stethoscope, this is known as auscultation. When the heart pumps blood, there are certain sounds associated with this function. Your veterinarian will listen for any abnormal sounds or rhythms that could indicate a potential problem.

One of the unusual sounds that your veterinarian might hear is a heart murmur. A murmur is not a disease in and of itself; it is a sound that is caused by turbulent blood flow within the heart. Blood typically flows in one direction but when it is disrupted due to certain cardiac abnormalities, it may become more chaotic or disorganized and flow in the wrong direction (referred to as turbulent). 

Qualities of the murmur can vary and may indicate problems in the heart, for example:

• the loudness (or intensity) of the murmur
• where in the heart cycle the murmur occurs
• how long or short the murmur is
• the location of murmur

All of these features give your veterinarian information about what the possible cause of the murmur might be, whether it merits further investigation, or might be harmless.

What causes heart murmurs in dogs?

A heart murmur is a sign of a disruption in the blood flow of the heart, and may indicate presence of a heart condition or it may be harmless.

Innocent murmurs 

Some murmurs are detected when puppies are young and tend to resolve by the time a dog is four to six months old. These murmurs, referred to as “innocent” murmurs,  have no negative impact on a dog’s health and are more common in the large breed dogs. One study found that approximately 30% of otherwise clinically-healthy puppies presented with an “innocent” murmur. 

Innocent murmurs tend to be soft, short and found in the absence of other heart abnormalities. They also tend to be found only when the heart contracts during the systole phase of the heart cycle..

Rating/grading of heart murmurs

Heart murmurs are graded on a scale from I-VI (1 to 6). The lower the grade, the quieter the murmur tends to be. Higher grade heart murmurs are louder and can be heard,or even felt, when listening to other areas of the heart during auscultation. 

Is it serious? And further diagnostics

Your veterinarian will let you know what to do if your puppy presents with a heart murmur. They may recommend a recheck after a certain period of time, or may refer you to a veterinary cardiologist for additional testing. This is common with higher grade murmurs, a murmur that is still present after the puppy is six months old, or if the murmur has progressed since a previous examination.

There are several tests that can help veterinarians better assess the functioning of the heart:

Echocardiograms/ultrasound

An echocardiogram performed by a board-certified veterinary cardiologist is considered the “gold standard” for assessing your dog’s heart health in real time. The cardiologist will be able to look at the structure and function of the heart. This is a non-invasive procedure that uses ultrasound.

Other tests:

• Chest x-rays (radiographs) can be used to assess the size, shape and position of the relevant tissues, organs and bones and in some cases whether a dog is experiencing congestive heart failure.
• Electrocardiograms (EKG/ECG) provide an assessment of the rhythm of the heartbeat, to look for abnormalities. A Holter monitor can be used to record the electrical activity of a dog’s heart outside of the office visit and for an extended period of time (e.g. 24 hours) if necessary. 
• A blood pressure check can assess if an animal is suffering from hypertension (high blood pressure) or hypotension (low blood pressure), which can occur with heart disease.
• Cardiopet ProBNP is a blood test that measures a hormone called NT-proBNP which is released by a specific type of cardiac cell (myocyte) when they are stressed or stretched.

Prognosis

The prognosis for puppies with an “innocent” murmur is excellent. For other dogs, the prognosis is highly dependent on the cause of the murmur. A veterinary cardiologist can assist you with making decisions about medication, management and monitoring of heart disease.

What if my dog needs anesthesia?

If your dog needs surgery, a dental, or other medical procedure, they may need to be placed under anesthesia. Although anesthesia is generally very safe, heart disease can increase some of the risks. In some cases, the veterinarian may choose a different anesthetic protocol or take other precautions, such as continual monitoring of blood pressure and blood oxygen during the procedure, to decrease those risks. 

It’s always best to know the underlying cause of the murmur first, so your veterinarian may recommend further diagnostic tests before scheduling a procedure.

Breeding

If you intend to breed your puppy and they present with a heart murmur, further diagnostics are strongly recommended, as many heart conditions are heritable. Many veterinarians recommend not breeding dogs with any heart murmurs or with murmurs above grade I because of the risk of passing a heart condition to the offspring. For bitches, pregnancy can also put stress on the heart. If your dog is a breed at high risk of heart disease, or has a heart murmur, we recommend discussing breeding plans with your veterinarian or a board-certified veterinary cardiologist. 

References

VCA: Heart Murmurs in Dogs

University of Illinois College of Veterinary Medicine: The Tell-tale Murmur Heart Problems in Puppies

University of Missouri Veterinary Health Center: Heart Murmurs

Sewell, D. (2016). Heart murmurs in puppies and kittens. Companion Animal, 21(7), 376-383. https://www.magonlinelibrary.com/doi/full/10.12968/coan.2016.21.7.376

Szatmári, V., van Leeuwen, M. W., & Teske, E. (2015). Innocent cardiac murmur in puppies: prevalence, correlation with hematocrit, and auscultation characteristics. Journal of veterinary internal medicine, 29(6), 1524-1528. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4895663/

van Staveren, M. D. B., & Szatmári, V. (2020). Detecting and recording cardiac murmurs in clinically healthy puppies in first opinion veterinary practice at the first health check. Acta Veterinaria Scandinavica, 62(1), 1-8. https://link.springer.com/article/10.1186/s13028-020-00535-1