Just as with humans, a dog’s heart health is an important component of their physical well-being. When your vet checks your dog’s heartbeat with a stethoscope, one of the key things they are listening for is a heart murmur. But what does a murmur mean for your dog, and what should you do if your vet finds one?
What Is a Heart Murmur?
Dog anatomy is similar to human anatomy in that the heart is responsible for pumping blood through the body. The heart does this with four chambers—two ventricles and two atria. To make sure blood flows in the proper direction, a one-way valve between each of these chambers opens and closes as blood fills a chamber, then empties out again. This is what gives the heartbeat its characteristic “lub-dub” sound.
An abnormal heartbeat sound is known as a heart murmur. It’s an additional whooshing noise caused by turbulence in the flow of blood as it passes through the heart.
Are There Different Kinds of Heart Murmurs in Dogs?
According to Dr. Claire Wiley, VMD, DACVIM, and Executive Director of the AKC DNA Program, heart murmurs in dogs are usually characterized by their intensity, timing, and the side of the chest where the murmur is heard. Intensity is rated with a grading system that ranges from grade I (the mildest) to grade VI (the most severe). “A grade I heart murmur is barely audible and may only be detected in a quiet room,” says Dr. Wiley, “while a grade VI murmur is very loud and can be heard with a stethoscope placed several inches away from the dog’s chest.”
But there is even more to describing a heart murmur. “In addition to the grading system, heart murmurs in dogs can also be characterized by the sound they make,” Dr. Wiley says. “For example, a systolic murmur is heard during the contraction of the heart, while a diastolic murmur is heard during the relaxation phase of the heart.”
Dr. Wiley stresses that not all heart murmurs in dogs indicate a serious problem. Some are completely harmless or benign. These “innocent” heart murmurs, also called physiologic murmurs, don’t typically require treatment. “However, all heart murmurs should be evaluated by a veterinarian to determine the underlying cause and whether or not treatment is necessary.”
Can Puppies Have Heart Murmurs?
Dr. Wiley says that innocent heart murmurs are often heard in young puppies and can be caused by factors such as changes in blood flow or increased heart rate during exercise or excitement. Plus, puppies’ hearts are still developing. Some breeds may even have a predisposition to innocent heart murmurs due to genetic factors or differences in their heart anatomy.
According to recent research on the identification and clinical significance of heart murmurs in puppies, an average of 28 percent of puppies under six months of age have an innocent heart murmur. That can rise to as high as 58 percent in puppies belonging to athletic breeds such as Whippets. Although it’s still important to have a veterinarian’s evaluation, Dr. Wiley assures people that these puppy heart murmurs are usually not associated with any underlying heart disease or abnormality. “In many cases, innocent heart murmurs in puppies will resolve on their own as the puppy grows and their heart matures. However, if a heart murmur persists or is accompanied by other symptoms, further evaluation and treatment may be necessary.”
What Causes Heart Murmurs in Dogs?
Besides innocent heart murmurs, dogs can also have heart murmurs that hint at something more serious. These can be caused by conditions that change the thickness of the blood, such as anemia, or that increase cardiac output, like hyperthyroidism. Problems with the heart, such as an infected heart valve or structural issues, can also be to blame. Dr. Wiley explains that structural issues can include problems with the heart valves, like aortic stenosis, a narrowing of the aortic valve, or congenital (present at birth) heart defects. “Other structural issues that can cause a heart murmur include holes in the heart, such as atrial septal defects or ventricular septal defects, and conditions that cause the heart muscle to become enlarged or thickened, such as hypertrophic cardiomyopathy.”
Mitral valve disease is a common cause of heart murmurs in dogs, particularly in older, small-breed dogs. This occurs when blood leaks back through the mitral valve (the normally one-way valve between the left ventricle and left atrium of the heart). Dr. Wiley says the earliest sign of the leakage is normally a heart murmur caused by the blood flowing backward through the valve. Initially, this condition causes no obvious clinical signs, but as it progresses, it becomes more severe and reduces the heart’s efficiency until congestive heart failure develops. “From the time a murmur develops, it may be a few months to several years until heart failure occurs,” she says. “Dogs typically succumb to the disease because they are unable to breathe or provide oxygen to their tissues.”
How Is a Dog Heart Murmur Diagnosed?
Because heart health in dogs is so important, it’s essential to provide your dog with regular veterinary check-ups so a murmur can be caught right away. For example, early detection and intervention are essential for managing mitral valve disease.
To detect a murmur, your vet will use a stethoscope to listen to your dog’s heart on both the right and left sides. “Ultimately, an echocardiogram by a board-certified veterinary cardiologist is required for definitive diagnosis,” Dr. Wiley says. “An ‘echo’ is an ultrasound of the heart and is used to visualize all four chambers and the heart valves.”
How Do You Treat a Dog Heart Murmur?
Some heart murmurs, such as innocent murmurs in growing puppies, require no treatment at all. But for other murmurs, treatment will be based on the underlying cause. That might include regular monitoring of your dog’s heart, medications, specialized diets, or even surgery to correct certain heart defects.
The prognosis or expected outcome of the diagnosis also depends on the underlying cause. The heart murmur might have no impact on your dog’s health, or it could dramatically shorten their lifespan. Speak to your vet or veterinary cardiologist about your dog’s specific condition so you can understand what to expect.