Myths and Misconceptions about Dogs with Heart Murmurs
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Myths and Misconceptions about Dogs with Heart Murmurs

by Rebecca Saunders, DVM, DACVIM (Cardiology)
Mar 1, 2021

Learning that your dog has been diagnosed with a heart murmur can be unsettling and leave you with several questions after your vet visit. This article aims to clarify common myths and misconceptions regarding heart murmurs in dogs so that any pet owner can understand the significance of this diagnosis and the next best steps.

What is a heart murmur?

A heart murmur is an abnormal sound that a veterinarian hears when listening to a pet’s heart with a stethoscope during a physical exam. Like people, an animal’s heart should have two distinct heart sounds: lub-dub, lub-dub, lub-dub. When an additional “whooshing” sound is heard between the normal heart sounds, this is called a heart murmur.

Does a heart murmur mean my dog has heart disease?

Not necessarily; not all dogs diagnosed with a heart murmur will suffer from cardiac (heart) disease. A heart murmur is a clinical finding—not a disease diagnosis. Some heart murmurs are benign or harmless and may go away on their own, particularly in puppies.

The only way to know the significance of your pet’s murmur is to work with your veterinarian and/or a Veterinary Cardiologist (specialist) to determine the cause of the murmur and the severity of the heart disease, if present. Additional diagnostic testing, such as an echocardiogram (ultrasound of the heart) will likely be required.

Will my puppy “grow out” of his heart murmur?

Some puppies can grow out of heart murmurs by approximately 16 weeks of age. These murmurs are usually low grade (quiet) and show no signs of affecting the animal. If your puppy has a louder murmur that has been heard at several vet visits, it is recommended that your pet be evaluated by a veterinary cardiologist to determine if intervention (medicine or surgery) is advised.

What causes a heart murmur in dogs?

Anything that changes the blood flow through the heart creating turbulence can cause a murmur to be heard. Some of the common causes of heart murmurs in dogs include:

  • Heart valve deficiencies (dysplasia)
  • Defects in the heart muscle walls (ventricular septal defect)
  • Infection of the heart valves (endocarditis)
  • Extra vessel connecting the great arteries (patent ductus arteriosus)
  • Narrowing of the pulmonary valve (pulmonic stenosis)
  • Narrowing of, at, or below the aortic valve (aortic/subaortic stenosis)
  • Thickening of the heart valves (myxomatous mitral/tricuspid valve degeneration)
  • Weakening of the heart muscle (dilated cardiomyopathy)

Does the loudness (grade) of the murmur correlate with the severity of heart disease present?

Not always. Murmurs are graded on a scale that refers to their loudness (see below). This scale is somewhat subjective since every veterinarian’s ears are different, but it is useful to describe murmurs and monitor them over time. Quiet murmurs may still represent severe heart disease in a patient, while conversely, loud murmurs may not impact a dog lifelong, depending on the diagnosis. This is why further investigation into the cause of the murmur with a veterinary cardiologist is useful to guide treatment recommendations and provide prognostic information.

  • Grade 1: heard inconsistently in a quiet room with a quiet animal
  • Grade 2: easily heard but quieter than the normal heart sounds
  • Grade 3: same intensity as the heart sounds
  • Grade 4: louder than the heart sounds and heard on both sides of the chest
  • Grade 5: loud with a thrill (vibration) that can be felt with the hand against the chest
  • Grade 6: very loud with a thrill and can be heard with the stethoscope off the body wall

My dog is acting normally. Does that mean the heart murmur is harmless?

Again, not necessarily. Dogs may be asymptomatic for their heart murmur but have significant heart disease already present that warrants treatment. Since acquired heart disease usually presents in older patients, owners often think they are slowing down due to age when heart disease is truly contributing to their change in energy.

In other cases, asymptomatic dogs with heart murmurs may not require heart medications, but they may have the early stages of heart disease present that warrant other precautions. For instance, general anesthesia for a surgery or dental procedure is only recommended if a dog diagnosed with a heart murmur has been evaluated by a veterinary cardiologist and deemed to be a safe anesthetic candidate with appropriate protocol precautions in place.

What are signs of cardiac (heart) disease in dogs?

Signs of cardiac disease in dogs can include:

  • Difficulty or labored breathing
  • Rapid, shallow breathing
  • Cough
  • Abdominal (stomach) distention (enlargement)
  • Inability to exercise/weakness
  • Blue gums
  • Collapse or fainting

Can my dog’s heart murmur cause a heart attack?

Signs of a heart attack in people include chest pain, shortness of breath and weakness. It’s scary to imagine our pets experiencing something so unpredictable and dangerous! Luckily, dogs do not have heart attacks in the same sense that humans do. Most human heart attacks occur when an artery is blocked and the heart cannot continue to pump blood; this same type of disease does not occur in dogs.

In some cases, dogs with heart disease will experience fainting (syncope). These episodes can resemble a heart attack, but do not often cause permanent damage and pets recover quickly.

What are treatment options for dogs with heart murmurs?

Treatment is designed to relieve the issues associated with heart disease related to the murmur. Some dogs with heart murmurs may live normal lives and never require treatment; others with more severe disease will benefit significantly from treatment, which can range from oral medications to surgery.

A veterinary cardiologist will tailor a treatment plan to improve your pet’s quality of life, as well as extend the time you have together. Depending on the cause of the murmur, treatment may sometimes “cure” the murmur. For example, if your dog is diagnosed with a patent ductus arteriosus (PDA), surgery can correct this abnormality, eliminate the heart murmur and a normal life expectancy is anticipated. This is why investigating the cause of a murmur with further testing by a veterinary cardiologist can be critical.

Will a healthy diet and exercise reduce my pet’s risk of developing heart disease when a murmur is present?

The most common form of human heart disease is Coronary Artery Disease (CAD). With this condition, cholesterol (plaque) accumulates resulting in narrowing or blocking of arteries in the heart. This can lead to heart attacks and strokes. In order to prevent high cholesterol, people are instructed to avoid fatty foods and exercise frequently.

Luckily, your pet’s heart disease is not caused by plaque in his or her arteries. Dogs are susceptible to two types of heart disease: heart muscle disease or heart valve disease, not CAD. While a balanced diet (that is not grain-free; a high quality kibble or canned food) is integral to your pet’s overall health, the standard human “heart healthy” diet will not prevent your pet from developing heart disease.

Because dogs’ heart disease is so different than that of humans, vigorous aerobic exercise such as running can actually put more strain on your pet’s heart. Based on diagnostic findings, your veterinary cardiologist may recommend reducing or limiting your pet’s activity to promote heart health and deter cardiac symptoms.

How do I have my dog’s heart murmur evaluated further?

Use the search tool to find a Veterinary Cardiologist in your area. Contact the hospital of your choice to discuss your pet’s condition.

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