Dog Heart Murmur Diagnosis, Treatment and Support

What Does it Mean When Your Veterinarian Tells You Your Dog Has a Heart Murmur?

A heart murmur is an abnormal heart sound made by the heart, typically a swishing sound made by choppy or turbulent blood flow. The four chambers of your dog's heart work together to pump blood to the lungs to pick up oxygen and then to the rest of the body to deliver that oxygen. Each of those chambers has a valve at the entrance and exit to prevent blood from flowing backward through the heart. When blood does not flow properly, it causes turbulence, which results in a swishy murmur sound. When your veterinarian listens to your dog's heart with a stethoscope, he or she may detect a heart murmur.

A heart murmur's intensity is graded on a scale from I to VI. This is how loud the murmur is. A louder murmur indicates increased turbulence in the heart, but it does not always indicate that the dog's condition is worse. Your veterinarian will also consider how long or short the murmur is, where it is coming from in the heart (determined by where the murmur is heard on the chest), and when it occurs during the heartbeat cycle.

Murmurs may be an "innocent heart murmur" (also called "physiologic" or "pathologic"). Innocent/physiologic murmurs have no symptoms or signs and have no effect on the dog's health. These murmurs are typically Grade I and are most common in young large-breed puppies.

The murmur may appear when the puppy is 6 to 8 weeks old and will disappear when the puppy is 4 to 5 months old.

Pathologic murmurs are caused by structural heart disease or by an external condition or disease that interferes with heart function. Your dog might have congenital heart disease (present at birth) or acquired heart murmurs (showing up later in life).

The majority of heart murmurs are systolic. Pulmonic stenosis or sub-aortic stenosis, which is a narrowing of the blood vessel that causes obstruction of blood flow, is the most common cause of systolic murmurs.

Causes of Dog Heart Murmurs

Some of the more common causes of heart murmurs in adult dogs and in puppies include:

Atrio-ventricular valve degeneration

This happens when the valve that separates the atrium and ventricle on one (or both) sides of the heart becomes weak and floppy and begins to leak. If the left side of the heart is affected, the condition is known as mitral insufficiency or mitral regurgitation; if the right side is affected by a leaky mitral valve, the condition is known as tricuspid insufficiency or tricuspid regurgitation.

This is the most common cause of acquired heart murmurs in dogs, especially in small breed dogs over the age of eight years. Owners frequently misdiagnose the symptoms as signs of aging and arthritis. When the chest is listened to with a stethoscope, almost all dogs with clinically significant mitral and tricuspid regurgitation will have a cardiac murmur heard. Virtually all dogs with clinically important mitral and tricuspid regurgitation will have a cardiac murmur heard when the chest is listened to with a stethoscope. Veterinarians can hear a murmur long (months to years) before clinical signs are noticed.

Subaortic stenosis

Subaortic stenosis is a narrowing of the area beneath the aortic valve where blood exits the heart to travel to the rest of the body. This narrowing can impair blood flow, requiring the heart to work harder to pump enough blood. Mild cases may not have any other symptoms, whereas moderate to severe cases may have symptoms from birth. It is possible to die suddenly. This is an inherited condition that is most common in large breed dogs. Treatment is often with a beta blocker medication.

Pulmonic stenosis

Pulmonic stenosis occurs when the leaflets of the valve that marks the exit of the right side of the heart where blood travels to the lungs thicken or fuse together. This is a congenital, inherited condition that can result in moderate to severe blood flow obstruction. Dogs with minor disease can lead normal lives. Dogs with advanced disease, on the other hand, may experience exercise intolerance, collapse, arrhythmias, or heart failure. When the chest is listened to with a stethoscope, almost all dogs with clinically significant pulmonic stenosis will have a cardiac murmur heard. The severity of this disease is often, but not always, correlated with the loudness of the murmur.  This condition sometimes is corrected with surgery.

Patent ductus arteriosus (PDA)

PDA occurs when a hole in the heart that existed in utero fails to close after birth. This has an effect on the flow of blood to the lungs to pick up oxygen. This hole is usually repaired surgically. When a veterinarian listens to your puppy's heart, he or she will notice a distinct sound caused by a PDA. This is an inherited disorder and sometimes warrants surgical correction.

Dilated cardiomyopathy

DCM is a disease called dilated cardiomyopathy. It occurs when the ventricle walls are thin, making them less efficient at pumping blood. The most common type of heart disease in large breed dogs.

DCM is thought to have an inherited component in some breeds, but other factors also play a role in its development. DCM, as you may recall, is the disease that prompted the Food and Drug Administration to start looking into canine diets due to the unusually high number of cases reported. The cause of the increase in canine DCM has yet to be determined.

Bacterial endocarditis

In this heart disorder, bacteria in the bloodstream infect a heart valve ( usually the mitral valve - degenerative mitral valve disease - or aortic valves, but any valve can be affected). Bacteria can enter the body through any infection, from infected wounds to severe periodontal disease. As a result, acquired dog heart murmurs develop.

Diagnosis of this chronic valve disease can be difficult, and treatment usually consists of a lengthy course of antibiotics. This condition can be avoided with regular dental care, including professional cleanings. Anemia and hypoproteinemia (lack of red blood cells and protein, respectively, in the blood, causing it to be thinner), fever, infection, pregnancy, obesity, and malnutrition are all conditions that can cause a heart murmur (also known as a "functional heart murmur."

Other common causes include heartworm disease and hyperthyroidism.

Heart Murmur Breed Predisposition

Symptoms Related to Having a Heart Murmur

If your dog has a heart murmur and any of the following symptoms, the murmur will be considered to be a high grade. If your puppy suffers from a PDA (hole in the heart), then a workup will be recommended to determine what is causing the murmur.

• Weight loss
• No or poor appetite
• Pale gums
• The dog doesn't seem well
• Reluctance to exercise
• Breathing difficulty
• Coughing or Hacking
• Fainting
• Collapse
• Heart arrhythmia, Irregular heartbeat or pulse
• Abnormal pulse
• Excessive panting (even if the dog is at rest)
• Severe water retention

When Should You Worry About a Heart Murmur in a Dog?

Typically, heart murmurs are discovered during a routine veterinary visit. When your veterinarian first notices a murmur, he or she will ask you questions about your dog's energy level and lifestyle habits to see if there are any early signs of heart disease. The severity of a murmur is determined by its characteristics and whether your dog has any other symptoms. This information will assist your veterinarian in making a diagnosis or referring you to a cardiologist.

Dog Heart Murmur Grades

Heart murmurs are graded based on severity:

Grade I: Hard to hear, soft murmur. Can often be heard from only one location on the chest.

Grade II: Moderately loud murmur that is noticed immediately.

Grade III: Moderately loud murmur that is immediately noticed when listening to the heart.

Grade IV: Loud murmur.

Grade V: Loud murmur that can be felt when a hand is pressed on the chest.

Grade VI: Loud murmur that can be heard with a stethoscope that is slightly away from the body.

Diagnosis

A heart examination will help to determine the cause of the murmur. The veterinarian will first determine if the murmur is heard on the left side or right side of the dog. In puppies the left side might be an "innocent murmur" that requires further evaluation after 6 months of age. This type of murmur is considered to be a normal part of early heart function. If the murmur is louder, it would require evaluation, possibly with an echocardiogram.

Keep in mind that a murmur is a symptom, not a disease. If a young puppy exhibits a soft murmur, your veterinarian will most likely advise you to return in a few weeks to see if the murmur is still present. If the murmur has vanished or softened, it is most likely innocent murmurs that will fade as she grows older. Adult dogs who are distressed during the veterinary exam may exhibit a murmur that disappears when the dog is listened to later when she is calmer.

A cardiac workup will typically include radiographs (x-rays) to assess the size and shape of the heart, an electrocardiogram (ECG) to assess the heart's electrical activity, and/or an echocardiogram (ultrasound of the heart) to assess the inside of the heart. A Doppler echo will also allow the practitioner to pinpoint the exact location of the murmur. Echocardiograms and Doppler tests are typically performed at a specialized clinic. Bloodwork will be performed to detect anemia, infection, or systemic illness.

Treatment

Dog Heart Murmur FAQ

How long does it take to diagnose a puppy with a heart murmur?

Veterinarians can usually diagnose a dog that is showing heart murmurs within 6-8 weeks of age.

Should You Adopt a Puppy with a Heart Murmur?

There is no simple answer to this question. Many low-grade (Grade I or II) murmurs in puppies will resolve before the puppy reaches the age of six months and are not cause for concern. If the puppy has a higher grade murmur and/or other symptoms of heart disease or illness, an echocardiogram is highly recommended to obtain an accurate diagnosis.

lf you have bought the puppy, and the murmur was discovered at her first wellness check review your puppy contract to see if the breeder, seller, or rescue offers any guarantee. See if you have time within your purchase agreement for a followup veterinary visit to see if the murmur has resolved on its' own or if the cause is one of the congenital heart defects.

If you haven't already purchased the puppy, talk to the breeder or resource about whether or not diagnostics will be pursued and who will pay for them. If you intend to keep the puppy and re-evaluate her later, make a plan for what will happen if the murmur does not go away. All discussions should be documented.

How Long Can a Dog Live with a Heart Murmur?

If the murmurs resolve, puppies live normal lives and seldom require veterinary treatment. If not, the murmur may require surgery, and the puppy will require veterinary visits to monitor her well being.

If the murmur does persist into puppyhood or beyond, the puppy will most likely suffer from heart disease or illness.

If your veterinarian detects the heart sounds of murmurs in a puppy that will live normal lives with no treatment, the puppy may live a short life expectancy if diagnosed early and treated, especially in puppies with heart murmurs diagnosed at 6-7 months.

Can a Heart Murmur be Fatal In Dogs?

In order for murmurs to be fatal, puppies must suffer from an extracardiac problem, meaning that their heart must fail and fail rapidly.

If this is the diagnosis, it is imperative to begin addressing the murmur as soon as the murmur appears so as to prevent the puppy from developing heart disease and/or dying from heart failure.

In the majority of murmurs, heart murmurs do not progress beyond a puppy being evaluated to determine whether or not treatment should be undertaken, so the murmur will usually resolve with time.

The most frequent causes of murmurs are extracardiac disease and/or defects.

Extracardiac disease and the defect causes murmurs to develop when the heart muscle does not receive enough oxygenated blood.

Your veterinarian may ask you to measure your dog's SRR (sleeping respiratory rate.) If the rate moves to higher than 30 breaths/minute, therapy might be needed for chronic heart failure (CHF).

Can the Sound of a Dog's Heart Murmur be Soft One Day and Loud Another Day?

Sometimes, murmurs will progress to become louder and louder. These louder murmurs will usually be determined to be due to the presence of an abnormal heart sound. Some murmurs are soft, quiet, and quiet again, and others are loud and loud.

The sound itself is typically determined by the length of the sound (usually between 60 – 140 bpm) and the timings of when it happens.  

Some murmurs, particularly those that develop later on in life, can have a loud sound and soft sound at approximately the same time.

Some murmurs can have soft sounds throughout their duration.  

Other murmurs are typically soft throughout their duration, but can suddenly change to loud sounds. These murmurs can also be determined by their timing.  

Can Heart Murmurs in Dogs be Treated?

There is no specific treatment recommended for heart murmur in dogs; however, they can usually be managed, and often resolve with time. Some dogs diagnosed with heart murmurs can be treated, usually by oral medications and/or surgery, depending on the diagnosis of the murmur.

Can a Heart Murmur be Fatal in dogs?

Pathological cardiac disease that causes heart murmurs usually progresses to congestive heart failure. This is a potentially fatal condition. Dogs with heart failure frequently have an accumulation of fluids in their lungs.

How Long Can Dogs Live With a Heart Murmur?

Many dogs live for many years after being diagnosed with a heart murmur, and some even live for years after being diagnosed with heart failure. If you dog has a leaky mitral valve, long-term use of medication can help to prolong dog life. If your dog has dilated cardiomyopathy, the prognosis varies based on grade.

Can Walking a Dog with a Heart Murmur be Bad for the Dog?

Dogs with a heart murmur are usually intolerant of hot and humid days, so they should go for short walks early in the morning. In the summer, you can use more mental exercise activities, such as puzzle games, to keep their mind stimulated.

What can I Feed my Dog with a Heart Murmur?

You should feed a dog with a heart murmur a heart-healthy diet that controls the levels of chloride and sodium (salt.). Do not feed a home-cooked diet unless it is balanced by a veterinary nutritionist, as there is a risk of too much salt in the diet. Consider a balanced diet made for canine cardiac patients, such as Hill's Prescription Diet h/d or Royal Canin Veterinary Diet Canine Cardiac.

Ask your veterinarian about Omega-3 fatty acids (fish oil or supplement) in the diet as DHA and EPA may help to stabilize cells in the heart.⁽⁴⁾

Can I Give a Dog With Heart Murmur Benadryl?

If your dog has any cardiovascular disease, consult with your veterinarian before providing Benadryl since an increased heart rate is a possible symptom. Benadryl is antihistaminic and makes dogs slightly sedated. It is generally safe in dogs with a slight heart murmur when used according to the veterinarian's instructions. Check with your veterinarian for the dose and if it is safe for your specific dog.(5)

The general dosing guideline according to the Merck Veterinary Manual is 2-4 milligrams of Benadryl per kilogram of body weight, two to three times per day. do not use time-release capsules. Also avoid liquid Benadryl since it contains sodium. If you are using children's Benadryl, ask your veterinarian for the dose.
Check with your veterinarian before providing any medications to your dog, particularly if your dog is showing any symptoms.

Can Dogs Fly with a Heart Murmur?

Dogs with heart conditions should be evaluated by a veterinarian at least one month prior to travel. Dogs become anxious during travel, subjecting the body to an unusual level of stress. If your dog is on heart medication you should be particularly cautious. A veterinarian will probably clear a dog to travel by air is the murmur is mile adn if there are no other health problems present.⁽⁶⁾

References

(1) Canine Heart Murmur; Clinical Brief, May 2021, Peer Reviewed