Updated on December 16, 2012
Heart Murmurs in Dogs: What Do They Mean?
I recently received the following question from Ardis, a reader who oversees a rescue organization in California:
One of our adopters has an older Beagle with a growth on his gum that is apparently not cancer and is not attached to the bone, but it is really impeding his ability to eat. The adopter is worried about the anesthesia to have it removed because the Beagle has a significant heart murmur. Do you have any opinions on ways to go for this lovely man and his dog?
This is such a great question and one that I want to answer for all of my readers because heart murmurs in dogs are so darned common. Normally when ausculting a dog’s heart (listening with a stethoscope), one hears a distinctive two beat “lub dub” sound with silence in between these two beats. In dogs with heart murmurs. A swishing sound or what I refer to as a “washing machine” sound is heard between the two “lub dub” beats.
Within the normal heart, blood flows smoothly through all four chambers. When the heart has a structural or functional defect, blood flow becomes turbulent and this turbulence is what creates the audible murmur. Heart murmurs are graded on a scale of I to VI depending on how loud they are. In general, the more turbulent the blood flow, the louder the heart murmur.
Mitral Valve Disease
Far and away the most common cause of canine heart murmurs is chronic degenerative mitral valve disease (aka, endocardiosis, mitral valvular insufficiency, mitral valve regurgitation, mitral valve degeneration). Normal mitral valves consist of two thin leaflets that separate the left atrium from the left ventricle. Their job is to open when the heart is filling with blood and seal tightly when the heart contracts, sending blood out into the body. Degenerative mitral valve disease causes clubbing and thickening of the valve leaflets rendering them unable to form a nice tight seal. As a result, when the heart contracts, some blood is “regurgitated” back into the left atrium. This abnormal blood flow creates an audible heart murmur, loudest over the left side of the dog’s chest.
Degenerative mitral valvular disease is thought to be an inherited condition and small breed dogs are particularly predisposed. In fact, my own little, six-year-old, 11 pound Nellie has mitral valve disease. Cavalier King Charles Spaniels are the “poster dogs” for this disorder- it is rare to find a Cavie over five or six years of age without a mitral murmur.
Thankfully, many dogs with mitral valve disease never develop any symptoms whatsoever. For the unfortunate others, abnormal blood flow increases the workload on the heart, ultimately resulting in heart failure symptoms (coughing, increased respiratory rate, labored breathing, exercise intolerance). Medications can successfully control the symptoms of heart failure for lengthy periods of time in most dogs.
Other Causes of Heart Murmurs
In addition to mitral valve disease, other causes of canine heart murmurs include congenital abnormalities (birth defects such as pulmonic stenosis, aortic stenosis, ventricular septal defects), chronic degenerative tricuspid valve disease (the tricuspid valve separates the right atrium from the right ventricle), and endocarditis (infection of a heart valve).
The best way to determine the cause of a heart murmur is with an ultrasound evaluation of the heart (echocardiogram). This study requires advanced equipment and operator expertise. If cardiac ultrasound has been recommended for your dog, be sure to seek out a veterinarian with specialty training. While ultrasound reveals the underlying cause of the heart murmur, X-rays of the chest cavity are the best way to determine if the dog is experiencing heart failure.
So, back to Ardis’ questions about the Beagle with a heart murmur and the growth on his gum. Here is the response I provided:
Many dogs have heart murmurs that do not, in any way, impair heart function. The best bet is to have this Beagle evaluated with cardiac ultrasound and chest X-rays, ideally performed by a veterinarian with advanced training in cardiology or internal medicine. These tests will allow his adopter to know the cause of his dog’s heart murmur as well as whether or not it will be safe to proceed with anesthesia. Just because a heart murmur is heard does not automatically mean the dog cannot be anesthetized. More information is needed before making this decision.
Does your dog happen to have a heart murmur? If so, please share what you know about it.
Wishing you and your four-legged family members a joyful and healthy holiday season.
Nancy Kay, DVM
Diplomate, American College of Veterinary Internal Medicine
Author of Speaking for Spot: Be the Advocate Your Dog Needs to Live a Happy, Healthy, Longer Life
Author of Your Dog’s Best Health: A Dozen Reasonable Things to Expect From Your Vet
Recipient, Leo K. Bustad Companion Animal Veterinarian of the Year Award
Recipient, American Animal Hospital Association Animal Welfare and Humane Ethics Award
Recipient, Dog Writers Association of America Award for Best Blog
Recipient, Eukanuba Canine Health Award
Recipient, AKC Club Publication Excellence Award
Become a Fan of Speaking for Spot on Facebook
Please visit http://www.speakingforspot.com to read excerpts from Speaking for Spot and Your Dog’s Best Health. There you will also find “Advocacy Aids”- helpful health forms you can download and use for your own dog, and a collection of published articles on advocating for your pet’s health. Speaking for Spot and Your Dog’s Best Health are available at www.speakingforspot.com, Amazon.com, local bookstores, and your favorite online book seller.