Heart Murmurs in Dogs: What Do They Mean?

Dr. Nancy’s Dog, Nellie

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.



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8 Comments on “Heart Murmurs in Dogs: What Do They Mean?

  1. My 14 year old Jack Russell named Princess has a heart murmur. We found out last year in May 2011 because she was having seizures. We took her to the vet because of the seizures and found out she had a grade 4 heart murmur. I don’t know how long she had the heart murmur. We went to the cardio for her and they said the heart murmur was caused from heart disease. Later that year in December 2011, she had another checkup and the cardio found a tumor in her spleen that had bled. He had special requirements if we did surgery for her like extra blood incase, anesthesia, etc. My regular vet didn’t want to attempt the surgery. I called a friend who manages a vet hospital and found out they would do it. She had the surgery two days before Christmas in 2011 and she is still here with us for this Christmas 2012. And the tumor was benign. She has gone for checkups since then at the cardio and she is on meds now. She seems to be perkier than she was last year.

  2. Dr. Kay,
    My 13.5 year old cocker mix has a low grade heart murmur. It was detected at about 2 years of age. We saw a cardiologist to determine if it was anything to worry about – and the ultrasound showed it was just a little change in speed in her blood flow (hopefully I’m stating this correctly). He said I didn’t need to worry and that it wouldn’t effect her. I never did have it rechecked with ultrasound down the road, but as she got older – after 8, it was more easily detected upon examination, but is still considered pretty low, like a 1 or 2. When she was about 8-9 and still had enough energy to chase a new puppy in the house, I would notice that she would cough during running. I assumed it was from the heart murmur. And now at 13.5 – it really is the least of my worries with her and doesn’t seem to effect her at all. Thank you for this informative article.

  3. My sweet Maggie was adopted at about age 2 with a level 2 murmur. We made the decision to have her die peacefully in my arms, earlier this year after a decade of fighting it. We treated her with medication and supplements and the last 2 years were tough. It’s a cruel disease and I am so sorry dogs continue to be bred that can pass it on to offspring.

  4. We have two Airedales with heart murmurs, one is nine years old, the other is six; the older one has had the murmur for at least five years; the other for about two years. They both have the same father but I am not aware of heart murmurs in that line.

    Both dogs are very active; both are very very healthy; and both do children’s programs with me to teach children about safety around dogs and how to be a responsible dog owner.

    Our vet for the last 14 years, Dr. Shelley Hempel in Sachse TX, checks them regularly and the only change in the heart murmurs is that they have gone down slightly, in both dogs from a two to a one and have stayed a one for at least a year. We do not expect the murmurs to disappear.

    These two dogs are a joy and we really don’t worry about the murmurs beyond having them checked whenever they have a vet visit. When the second one was diagnosed, I asked the vet what to do. Since the older one checked out as a one that day, when she had been a two the previous time she was checked, the vet told us to just do for the younger dog what we were doing for the older dog.

    I wonder, however, what is happening in the environment that might be part of the increase in heart murmurs. I have had Airedales for more than forty years and I have never had one, until these two, with a heart murmur. We lost an Airedale last year at the age of 15; she never had a heart murmur, and she was the mother of the younger dog we have now. Our dogs are raw fed, kept in excellent weight (you can always feel their ribs and backbone but you can never see them), get plenty of exercise, are very well trained, and they are a continual joy to us.

    I really appreciate the work you do and the knowledge you pass on to us dog lovers.

    Thank you.

  5. Dr. Kay My last three dogs have passed with mitral valve disease. Once diagnosed they each had about another 1 or 2 years. We did x-rays and you could see the heart enlarging each time. Very scary.

    You talk about it being inherited. I definitely agree. The three were father, daughter and granddaughter. I not have his great grandson and I close my eyes every time my vet checks his heart. He will be 12 next month and just had him checked a couple of months ago and so far no murmur.

    As you may remember, I work with IVDD dogs, but having 3 with MVD, I think it is every bit as traumatic as IVDD. You can treat and yes they can have a quality of life with the meds, but in the end it is very sad to watch them having trouble breathing and the other symptoms that develop.

    Thank you for bringing this to the attention of others.

  6. I’ve had several Cavaliers over the past 28 years and all but one eventually developed MVD. Yes, they can be safely anesthetized by an experienced vet – the recommended anesthesia usually being Isoflurane. Many years ago, my vet anesthetized my 13 yr old Cavalier with a Grade 6 murmurs (was on vasotec and lasix) and whose infected teeth were causing kidney failure. He was put on Anitrobe for 2 weeks prior to the dental in order to get as much infection out of his mouth as possible. All teeth except his molars were removed and the vet shot penicillin around the molars. He lived another 14 months with a much higher quality of life.

  7. my collie was born with a loud heart murmur. At 10 months of age I had an echocardiogram as well as x rays and they dye they put in to have her evaluated, before putting her under to spay her. Her results were sent to a board certified cardio vet in St Louis as the cardio vet performing the tests was baffeled. My collies heart was not enlarged, showed no leakage of blood anywhere and looked normal. The St Louis vet thought she probably had a small hole between the chambers on the back side where it wasnt visable. He figured she’d never have any problems with it. The collie is now 3 1/2 years old , does agility, herding, rally, formal obedience and is very active. She has never had any symptoms of heart problems.