Having your veterinarian pause while listening to your pet’s heart to tell you they hear a murmur can be scary. A heart murmur can indicate a serious underlying disease, but not in every case. Before you start losing sleep over the news of abnormal heart sounds in your dog, here’s what you need to know about heart murmurs in pets.
What is a heart murmur in dogs?
When a clinician listens to your dog’s heart with a stethoscope, they are listening for the two distinct sounds that occur from the closing of the valves of the atria and the ventricles, often described as ‘lub-dub’. A heart murmur is an abnormal heart sound, distinct from the normal ‘lub-dub.’
This abnormal heart sound is cause by turbulent flow of blood. Normally blood marches from the right atrium to the right ventricle to the lungs, to the left atrium and finally to the left ventricle, which pushes blood to the body.
If there is an abnormal structural change to the heart, instead of an orderly flow of blood from chamber to chamber, the blood can become turbulent. This makes an audible sound, often described as a whooshing sound.
What causes heart murmurs in dogs?
Abnormal heart sounds in dogs can be caused by a variety of different structural abnormalities. Anything that disrupts the normal flow of blood can potentially be heard with a stethoscope.
Degenerative Mitral Valve disease, for example, is one of the most common causes for a heart murmur diagnosed in older dogs. The mitral valves are arguably the hardest working valves in the heart. They’re the ones that close off the left ventricle, helping to push blood throughout the body. Over time they can start to leak, allowing blood to escape back to the chamber it came from. Little breed dogs are overrepresented for mitral valve disease, but this disease can occur in any breed.
In addition to leaky valves, narrowing of one or more of the great vessels or its entrance can cause turbulent blood flow. Subaortic Stenosis is an example of a structural change that can cause turbulent flow of blood and an audible murmur.
Vessels that aren’t supposed to be a part of the normal cardiac structure, such as a Patent Ductus Arteriosus can cause abnormal blood flow as well. This abnormality is caused by a vessel between the aorta and the pulmonary artery that normally closes at birth. It causes a classic sounding heart murmur that is continuous and often described as a washing machine sound.
Another common cause for a heart murmur is a defect (hole) in the septum (wall) of the heart. You can imagine a hole between two chambers would allow blood to move across the septum, causing turbulent flow of blood.
How are heart murmurs in dogs diagnosed?
Heart murmurs are generally diagnosed by auscultating the heart with a stethoscope. Veterinarians are trained to recognize abnormal heart sounds, and listening to the heart is an important part of a routine physical exam.
Some heart murmurs have a sound that can be classic for certain diseases, for example a Patent Ductus Arteriosus murmur has a very distinct way of sounding. That being said, the majority of the time it is impossible to determine the cause for the abnormal heart sounds without additional diagnostic testing.
Your veterinarian may recommend an echocardiogram, EKG, and chest radiographs to better understand what is causing the abnormal sound. An echocardiogram uses an ultrasound to image the chambers of the heart. An EKG looks at electric conductivity across the heart muscles and x-rays show the size and shape of the heart muscles.
With these extra tests, a correct diagnosis can be made, which is crucial for implementing a treatment plan and to better understand how serious the problem is.
What is the life expectancy of heart murmurs in dogs?
A diagnosis of a heart murmur means there is structurally something wrong with the heart (except for in innocent murmurs!). How dangerous this is for your pet depends on what is abnormal and how abnormal it is. Some heart defects are not compatible with life, others can be compensated for years, or may never cause a problem at all!
In general, as the blood flow is turbulent, the heart compensates for it by building more muscle. This works for a while, but eventually can cause the chambers to be too small, or the walls to be too stiff, decreasing the contractility of the heart itself. Over time, the heart will start to fail, causing fluid build-up in the lungs and subsequent respiratory failure.
How are heart murmurs in dogs treated?
The treatment for heart murmurs in dogs depends on what is causing the murmur. Some murmurs don’t require any treatment at all and the pet can live a normal comfortable life. Mitral valve disease, for example, is generally not treated until it starts causing problems, such as hypertrophy (thickening and enlarging) of the heart muscles and congestion (fluid buildup) in the lungs.
Some cardiac defects, such as a Patent Ductus Arteriosus, can be repaired surgically by a trained veterinary cardiac surgeon.
If the problem in the heart eventually leads to heart failure, there are medications that can be instituted to help the heart muscles work more efficiently.
Can heart murmurs in dogs be prevented?
The short answer is usually no, most heart murmurs cannot be prevented. There are some breeds that are much more prone to heart problems. Small breed dogs such as poodles and Chihuahuas, for example, commonly develop heart murmurs with age. A hereditary component is implicated in many other heart defects, and certain pure breeds, such as the Boxer and King Charles Spaniels, are overrepresented.
Recently the FDA has warned that diets labelled as ‘Grain Free’ can lead to heart disease in dogs1. There is enough evidence to suggest that feeding a grain inclusive diet is one way to prevent a rare form of heart disease in dogs.
Considering pet insurance is a great way to help prevent financial constraints from allowing you to have the best veterinary care for your pet. Veterinary diagnostic testing can be expensive, and insurance such as Pets Best can help keep your pet healthy.
1Freeman, L. M., Stern, J. A., Fries, R., Adin, D. B., & Rush, J. E. (2018). Diet-associated dilated cardiomyopathy in dogs: what do we know?. Journal of the American Veterinary Medical Association, 253(11), 1390-1394.