Heart Murmurs In Dogs: Grades, Symptoms, Treatment & More

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veterinary doctor is consulting a little dog checking for a heart murumer with a stethoscope

Hearing from your veterinarian that your dog has a heart murmur is, understandably, a scary moment. After all, no one wants to hear that their dog has a potential health issue. So, it’s natural that before understanding more about their condition, you may fear the worst. However, dog heart murmurs can mean a lot of things, and the prognosis for a dog or puppy with a heart murmur can be very variable. Some may require immediate treatment, while others may not cause a problem at all and could disappear with time. So, what is a dog heart murmur? What causes them, and what does it mean for your dog if they have one?

What is a heart murmur in dogs?

Simply speaking, a heart murmur is an extra heart sound. In dogs, the heart makes two sounds as the muscles contract and the heart valves close, creating the distinctive ‘lub-dub’ sound. A heart murmur is an extra noise before, after, during, or between the ‘lub-dub’ and is often described as a ‘whoosh.’ This noise is due to turbulent blood flow through the heart and is graded from I to VI according to how loud it is.

Different breeds are prone to different types of heart problems. For instance, the Cavalier King Charles Spaniel is particularly prone to mitral valve disease, as are many other small breeds of dog, while Dobermans, Cocker Spaniels, and some other large and giant dog breeds are prone to dilated cardiomyopathy. Top 10 dog breeds affected by heart problems are:

  1. Cavalier King Charles Spaniel
  2. Dachshund
  3. Miniature Poodle
  4. Doberman Pinscher
  5. Boxer
  6. Golden Retriever
  7. Schnauzer
  8. Great Dane
  9. Irish Wolfhound
  10. Labrador Retriever

Heart murmur grades in dogs

  • Grade I – A grade I heart murmur can only be heard in perfectly quiet conditions and if the stethoscope is placed in exactly the right place on the chest. It is very focal, and the sound does not radiate elsewhere.
  • Grade II – A grade II heart murmur can be heard easily with a stethoscope but is very soft. Like a grade I heart murmur, the sound is focal.
  • Grade III – A grade III heart murmur can be heard easily with a stethoscope and is moderately loud. Rather than being focal, you might be able to hear it in the region surrounding the point of maximal intensity (PMI).
  • Grade IV – A grade IV murmur is loud and can usually be heard with a stethoscope in multiple areas on both sides of the chest. However, it cannot be felt by placing a hand on the chest.
  • Grade V – A grade V murmur is loud, can usually be heard throughout the chest, and can be felt as a ‘thrill’ when a hand is placed over the heart. However, if the stethoscope is lifted off the skin, the murmur cannot be heard.
  • Grade VI – A grade VI murmur can be heard loudly throughout the chest, and the thrill is felt easily. It is so loud that it can be heard even with the stethoscope lifted off the chest.

What causes a dog heart murmur?

A dog heart murmur isn’t a diagnosis but more a symptom or clinical finding related to an underlying condition. Here are some of the possible causes of a heart murmur:

A hole in the heart

A hole in the heart, also known as a ventricular septal defect or an atrial septal defect, can cause blood to flow between the two sides of the heart. This is heard as a murmur and may or may not be accompanied by other symptoms.

An abnormal blood vessel

The Ductus Arteriosus is a tiny vessel that is present in puppies when they are in the womb. It allows blood to bypass the lungs since the pup is not breathing or requiring oxygen via this route yet. In most puppies, the vessel closes itself around the time of birth. However, very occasionally, the vessel remains, and blood continues to flow through the vessel. This is known as a Patent Ductus Arteriosus (PDA), and surgery is usually needed to manually close the vessel.

A leaky heart valve

One of the more common causes of heart murmurs is a leaky heart valve. If the valves between the atria and ventricles don’t form a tight seal, blood can flow from the ventricles back into the atria rather than around the body or to the lungs. This stream of backflowing blood forms a high-velocity jet, which causes the murmuring sound.

A narrow vessel

Sometimes, the vessels that lead out of the heart (the aorta and the pulmonary artery) can be narrowed at their connection with the heart. This is because there are natural valves in this position to prevent backflow. However, if these valves are too effective, they can obstruct blood from leaving the heart, causing a murmur due to the resistance and pressure.

A change in chamber size

Certain conditions, including Dilated Cardiomyopathy (DCM), cause the heart ventricles to become enlarged and ‘baggy.’ This can sometimes create turbulent flow and cause a murmur, although not all dogs with DCM will have a heart murmur.

A change in blood thickness

The flow of the blood through the heart can be altered if the viscosity changes (i.e., it is thicker or thinner in consistency). This can create murmurs.

Anemia

An example of a murmur caused by a change in viscosity is a ‘hemic murmur.’ When a dog is anemic, their blood is thinner because there are fewer red blood cells, and a murmur can be heard at very low levels.

Other Causes

A heart murmur may also be caused by heartworm infestation or a tumor of the heart tissue.

What causes a heart murmur in puppies?

Puppies can be affected by many of the heart murmur causes listed above. However, many murmurs in puppies are not a sign of a heart problem or poor health but a physiological murmur that will disappear with time.

If your vet hears a heart murmur while examining your puppy, they will check for other symptoms and assess their overall health. If there are no obvious concerns and the murmur is low-grade, they are likely to recommend a return visit in a month or two to check that the murmur has gone or improved. If there are any concerns that it isn’t a puppy murmur, they may recommend a heart scan to check.

What are the symptoms of a heart murmur in dogs?

If your dog has a heart murmur, they may not have any symptoms at all. However, here are some of the signs of an advanced-stage heart murmur in dogs that you should keep an eye out for:

  • Coughing – Dogs with a heart murmur may eventually develop congestive heart failure. This causes fluid to build up in the lungs, known as pulmonary edema, which leads to a soft, moist cough.
  • Exercise Intolerance – Dogs with heart failure may be less keen or able to run and play, and they may tire more easily or experience panting.
  • Elevated breathing rate at rest – There are lots of situations where your dog’s breathing rate could change due to excitement or exertion. However, if they’re breathing more rapidly while they’re sleeping, this could be due to heart failure.
  • Pale or purple/blue gums – Blood that doesn’t contain enough oxygen may look purple-ish blue. This is called cyanosis and is noticeable on the gums.
  • Lethargy – Dogs with weak hearts can become more tired and are commonly known to nap more than an average dog of the same age. This can also be evident in a reduced ability to exercise, as mentioned above.
  • Collapse – Also known as syncope, some cardiac conditions can lead to fainting episodes if the circulation isn’t providing enough oxygen to your dog’s organs and tissues. If your dog has an episode of collapse, your vet will ask questions to identify exactly what happened. This will help them rule out other similar incidents like seizures or mobility problems.

Is there a dog heart murmur treatment?

Depending on the cause of your dog’s heart murmur, there may not be any required treatment. If the cause is related to the heart, but the murmur is low grade, with no changes to the heart function and no symptoms being displayed, all that is required is close monitoring.

Your veterinarian may recommend regular heart scans to check the heart’s appearance and function, and they’ll want you to keep a close eye out for symptoms.

Some medications help delay the onset of symptoms, but they must be given at the right stage of the disease. If your dog is showing symptoms of heart failure, or if there is an identifiable, treatable cause like heartworm or anemia, treatment will be required.

Surgery

Surgical treatment for heart murmurs is sometimes an option, depending on the cause. For example, if the cause of the murmur is a narrowing of one of the blood vessels leaving the heart, like pulmonic stenosis or aortic stenosis (both very serious heart conditions), a special catheter with a balloon can be passed through the vessel, and gently inflated, expanding the narrowed area and relieving any obstruction.

If your puppy has a patent ductus arteriosus, where one of the fetal vessels that should close at birth stays open, surgery can be performed to close the vessel. Similarly, mitral valve disease, where the valve between the left atrium and ventricle doesn’t form a good seal, can now be treated in some top hospitals with specialist surgery to replace the valve.

What medication is used to treat heart murmurs in dogs?

The medication used to treat a heart condition in dogs will vary, depending on the diagnosis. If a dog has a heart murmur due to a leaky valve but isn’t showing symptoms of heart failure yet, they may benefit from a medication that helps the heart muscle pump more effectively.

However, given at the wrong stage of the disease, this could cause deterioration. Once heart failure has developed, a dog may also require medication to alter their blood pressure, control their heart rhythm, and remove fluid from their lungs, chest, or abdomen (like water tablets in people). Unfortunately, there is no cure for heart disease in humans or in dogs.

Heart murmur in dogs: life expectancy

The life expectancy of a dog with a heart murmur depends on the cause of the murmur and the stage when it is found. If found early and treatment started at the right time, dogs can live for several years on medication. However, if their heart function is severely affected and medication doesn’t cause an improvement, dogs may be less likely to live very much longer.

Can Pet Insurance Help Treat A Dog Heart Murmur?

Yes, we have heard many stories of how pet insurance helps owners manage the terrifying reality of a heart murmur in their dog. However, owners must have an active pet insurance policy with this coverage in place before the condition is diagnosed since most companies do not cover preexisting conditions.

According to Fetch Pet Insurance, Cavalier King Charles Spaniels are commonly treated for heart murmurs, mitral valve insufficiency, and seizures. Fetch’s claims show that the average cost for these illnesses is as follows:

  • Heart murmurs: $990
  • Mitral valve insufficiency: $1,143
  • Seizures: $1,454

Frequently Asked Questions

How do dogs get heart murmurs?

Dogs can be born with structural abnormalities of the heart or associated vessels, which can lead to heart murmurs from birth. However, some heart murmurs are acquired if a valve changes shape or another heart condition develops.

Can anxiety cause heart murmurs in dogs?

Anxiety might make a low-grade murmur easier to hear, but it cannot cause a heart murmur where there isn’t one.

Are heart murmurs common in older dogs?

Heart murmurs are more common in older dogs, but dogs of any age can have them. Many puppies have innocent physiological murmurs that disappear as they grow.

Managing Heart Conditions

Heart murmurs in dogs are very complex, so it’s understandable that, as a pet parent, you might be confused and overwhelmed when told your dog has one. Rest assured that your veterinarian will give you the information and guidance you need to keep your pet as healthy as possible for as long as possible. Your vet will most likely recommend you schedule an appointment with a cardiologist who can take echograms and further examine your dog’s heart condition and give you more detailed treatment options based on the grade and cause. Learn more about other heart-related topics, including grain-free dog food diets and how to perform CPR on your dog.

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The information provided through this website should not be used to diagnose or treat a health problem or disease; it is not intended to offer any legal opinion or advice or a substitute for professional safety advice or professional care. Please consult your health care provider, attorney, or product manual for professional advice. Products and services reviewed are provided by third parties; we are not responsible in any way for them, nor do we guarantee their functionality, utility, safety, or reliability. Our content is for educational purposes only.

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