Heart Murmur in Dogs - Should I Be Worried?

Heart Murmur in Dogs - Should I Be Worried?

Author WDF Staff


Taking your dog for a vet check-up can be pretty stressful as it is, but receiving a diagnose that your vet observed a heart murmur in your dog can be chilling. You didn’t need to finish vet college to know that hearts are very important. There are probably a million questions running through your mind. Still, before you panic, there are some things you should know about heart murmurs in dogs and how dangerous they are.

What are they?

To understand what a heart murmur is, first, we need to know how a heart works. Similar to humans, the dog’s heart pumps blood and sends it all over the vascular system. If everything is fine with the heart, the vet should hear a rhythmic beating through the stethoscope.

If the heart works as it is supposed to, the vet should hear a unique sound of opening and closing the heart valves. According to MyVet Hospital, the sound the vet should hear should be “lub-dub.” However, if there is something wrong with the heart, like the heart murmur, one part of the lub-dub sound will be replaced by “swoosh.” The swoosh sound means there is some issue with the blood flow from or to the heart.

Heart murmurs are not a disease; they usually point to a different health issue that is troubling your dog. Several reasons might happen, and not all heart murmurs are equally dangerous or serious. Dog owners should keep that in mind before they start imagining the worst possible scenarios.

Types of heart murmurs

Vets have broken these murmurs down for a better understanding of the conditions different heart murmurs can represent. There are three types of heart murmurs, and they are: diastolic, systolic, and continuous.

  • Diastolic - Diastolic are happening when the heart is relaxed. It happens between two heartbeats.
  • Systolic - Systolic are happening when the heart contracts.
  • Continous - As the name suggests, continuous murmurs are happening continuously throughout the heart’s relaxed and contracted phase.

vet examining dog

This is the first thing your vet will notice. The second thing they will do is grade heart murmurs on a scale that can index how loud and noticeable the murmur is. Vets have divided the classification into six separate grades;

  • Grade I - These are the weakest, barely detectable by a stethoscope.
  • Grade II - These are described as soft but noticeable.
  • Grade III - These are of medium loudness. Most murmurs connected to severe health issues are a minimum Grade III.
  • Grade IV - These are classified as reasonably loud. They can be detected on both sides of the chest.
  • Grade V - Classified as very loud. Easily detectable and can even be felt by a hand placed on the dog’s chest.
  • Grade VI - The loudest and most serious murmurs. They can be felt by hand, and this should be treated as a severe health concern.


When the vet is examining the dog, they may start describing how a murmur sounds. That is how they are configured and will help the vet diagnose the problem. There are four different configurations, and they are called crescendo-decrescendo, decrescendo, plateau, and machinery.

  • Crescendo-decrescendo - These get louder than quieter. They are associated with pulmonic and aortic stenosis.
  • Decrescendo - These ones start loud and get quieter. They usually point to a problem like aortic valve insufficiency or a ventricular septal defect.
  • Plateau - Plateau murmurs are consistently loud and are usually associated with aortic valve insufficiency.
  • Machinery - These are constant (continuous) murmurs, and they are associated with patent ductus arteriosus (PDA).

Receiving so much information at once can seem overwhelming and confusing. Vets made different classifications and names for heart murmurs. That way, they can get a more precise diagnosis and know how to move forward.

What are the most common causes of heart murmurs?

There are many reasons dogs may develop heart murmurs, and the exact breed, age, and health test results will point the vet to the right reason. There are three main categories of causes for this issue, and they are:

  • Disturbances caused by abnormal valves or vibrations
  • Disturbances caused by obstruction, diseased valves, or dilated vessels
  • Disturbances caused by a regurgitant flow

The exact reason will probably require extensive testing. Different diseases, parasites, or deformations can cause them, so your vet might not be absolutely sure before these tests are made.


The vast majority of heart murmurs are systolic, and they are mostly connected to pulmonic stenosis or subaortic stenosis. Other possible reasons are;

  • Anemia
  • Endocarditis of the mitral and tricuspid valve
  • Hyperthyroidism
  • Aortic valve insufficiency
  • Cardiomyopathy
  • Heartworm disease
  • Mitral and tricuspid heart failure
  • Systolic anterior mitral motion (SAM)


These types of heart murmurs are relatively rare in dogs, and the ones that are observed are mostly connected to aortic insufficiency, aortic and pulmonic valve endocarditis, and mitral and tricuspid valve stenosis.


Continuous heart murmurs are mostly associated with PDA, aortic regurgitation, and aortic stenosis with aortic regurgitation. However, there is a possibility that the heart murmurs are innocent.

What are innocent heart murmurs?

These heart murmurs are usually found in puppies, and as the name suggests, they have no impact on the puppy’s health. They should be monitored, but these heart murmurs usually resolve themselves over time. They are nothing to be worried about, and you will most likely have a healthy and happy puppy.

We are well aware that getting so much information can be confusing. Heart murmurs can point to different things, and you can never be sure why they are happening to your dog. Keep in mind the most essential thing in these situations - the vet is your ally.

Ask them for advice and guidance. They can narrow the diagnose for you and let you know what the most likely cause of your dog’s heart murmurs is. Follow their instructions, and we are sure your dog will be fine.

World Dog Finder team

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