Heart murmurs in dogs – What is it and what are the main causes?

Published by Amber LaRock

Updated on

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What is a heart murmur in dogs? 

A heart murmur in dogs is the irregular heartbeat sound that’s heard when listening to a dog’s heart with a stethoscope. When a dog’s heart is functioning properly, you can hear a clear and concrete heartbeat. When the heart is compromised, it can result in abnormal turbulent blood flow. 

heart murmurs in dogs

Abnormal turbulent blood flow can occur when blood passes across abnormal valves or structures in the heart, or when blood passes quickly through structures within the heart. Once these actions occur, the result is a heart murmur. 

Types of Heart Murmurs

When it comes to heart murmurs in dogs, there is a list of possible causes behind the abnormal turbulent blood flow. Since there are multiple conditions that can result in a murmur, they are generally split into three categories based on the timing of the heart murmur. These types include: 

  • Systolic: A murmur that takes place when the heart muscles contract. 
  • Diastolic: A murmur that occurs when the heart muscle is relaxed in between beats. 
  • Continuous: A murmur that occurs throughout the dog’s regular heartbeat cycle. 

Some other ways you can categorize heart murmurs include:

  • Physiologic heart murmur: A physiologic heart murmur is a murmur that does not affect the dog’s health. For example, puppies can experience low grade heart murmurs without any symptoms or clinical signs. These murmurs are mild, and usually resolve by 4-6 months of age.
  • Acquired heart murmur: In an acquired heart murmur, the murmur develops at some point during the dog’s life. While there are factors that can contribute to this, it’s often the result of developing heart disease. 
  • Congenital heart murmur: A congenital heart murmur is a murmur that is present from birth, and are often associated with heart defects that a dog was born with. 

Grades of Heart Murmurs in Dogs

Heart murmurs are measured in grades, which determine their severity according to a one to six grading scale. 

  • Grade 1 heart murmur: This murmur is the least severe, and is often not even heard with a stethoscope. 
  • Grade 2 heart murmur: These murmurs are still quite hard to hear for some veterinarians, since they are soft, but they can be heard with the help of a stethoscope. Veterinarians may only hear this murmur on certain sides of the chest.
  • Grade 3 heart murmur: This is when the murmur begins to increase in severity, and can begin to show clinical signs. 
  • Grade 4 heart murmur: These murmurs are quite obvious, and can be heard on both sides of the chest.
  • Grade 5 heart murmur: These murmurs are loud, and can be heard distinctly on either side of the chest. You can sometimes feel these murmurs when holding the dog’s chest. 
  • Grade 6 heart murmur: These murmurs are the most severe, and can be easily heard with a stethoscope and felt when holding the dog’s chest. 

Heart Murmur Configurations

Heart murmurs in dogs are made up of four main qualities or configurations.

  • Crescendo- Decrescendo murmurs: These murmurs alternate sounds by getting louder and then softer.
  • Plateau murmurs: These murmurs have a uniform sound and loudness.
  • Decrescendo murmurs: These murmurs start of loud and then get softer.
  • Machinery murmurs: These murmurs are continuous and occur throughout the heartbeat cycle.

The differences in sounds can be difficult to note at times, and is one of the many reasons why your veterinarian will recommend seeing a cardiologist. 

What are the causes for Heart Murmurs in Dogs?

Longer than the list of heart murmur categories in dogs, is the list of possible causes behind a heart murmur. Some conditions that cause heart murmurs in dogs include: 

  • Heartworms: A parasite that’s present in the circulatory system in dogs. 
  • Anemia: A reduction in the number of circulating red blood cells. 
  • Hyperthyroidism: The overproduction of the thyroid gland in dogs. 
  • Cardiomyopathy: Weakening of the muscles of the heart wall.
  • Endocarditis: An infection of the heart valves.
  • Tumors: Growths in the chest that can affect the heart’s function.
  • PDA: Congenital heart disease in dogs.
  • Defects in the heart wall: Abnormalities within the walls of the heart.

These are only the most common causes for heart murmurs in dogs, and are certainly not the only possible factors. 

Symptoms Of Heart Murmurs

Heart murmurs in dogs are not always symptomatic, but some of the most common complaints include: 

  • Coughing
  • Breathing difficulties
  • Congestion in their breath sounds
  • Fainting episodes
  • Lethargy or weakness
  • Distended abdomen
  • Blue or cyanotic gums

heart murmurs in dogs

If you notice any of these symptoms in your dog, it’s important to have them seen by a veterinarian as soon as possible. When dog’s present in distress from congestive heart failure, their owners often recall a slight cough leading up to that point. By diagnosing a heart murmur early, you can begin management before it becomes severe.  

Diagnosing Heart Murmurs

There are many steps in accurately diagnosing and finding the cause of a heart murmur. First, the veterinarian will hear the heart murmur upon physical exam. From that point on, they will suggest a series of diagnostics that may be performed in house or through a specialist, depending on what you have access to at your clinic. Recommended diagnostics include:

  • X-rays
  • Blood work and heartworm test
  • ECG
  • Blood pressure tests
  • Cardiac ultrasound

heart murmurs in dogs

Since there are a list of possible causes behind a heart murmur, your veterinarian will often recommend a trip to the cardiologist, if even just to confirm your current management plan.

Treatment of Heart Murmurs in Dogs

Treatment for heart murmurs in dogs will depend entirely on your dog’s symptoms and diagnosis. 

If a heart murmur is detected, but no symptoms are present, they may choose to just monitor your dog closely until symptoms arise. However, if your dog has symptoms, they will often recommend daily medications to manage their condition.

For dogs that present in crisis or respiratory distress for any reason, diagnostics and hospitalization will the recommended course of action. 

The most important way to come to an accurate prognosis is by finding the cause of a dog’s heart murmur. By treating the condition effectively, a dog will have a much better chance at recovery and management. 


Though heart murmurs in dogs should be taken seriously, there’s not always a need to panic. As long as your dog attends their yearly physicals and you have them seen at the first sight of symptoms, you can help to reduce the risk of heart murmur complications. 

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Amber, a dedicated animal enthusiast, has seamlessly merged her passion for animals with her career as a Licensed Vet Tech and content creator. Her journey is a testament to her commitment to educating pet parents through informative articles. With a degree in Veterinary Technology, she has become a prolific writer and a professional dog trainer. Amber's expertise spans veterinary medicine, pets, and shelter medicine. Her Amazon published book, "Heal My Fractious Heart - A Vet Med Romcom," showcases her creative writing talents. Currently residing in Chiang Mai, Thailand, she manages marketing and social media for a preventive pet health subscription company called Vetted.


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