Heart Murmurs in Dogs

I will be pulling down some statistics from private practice. Kind of like “what I see“ and I am not going to go back to some literature of global norms.

Heart Murmurs in Dogs

A heart murmur “happens” when one of the valves in a dogs heart doesn’t fit. So it leaks, and that makes an audible ‘murmur’. Murmurs are graded on a scale of one, to five. (1-5)

Every grade of heart murmur costs the dog 10% of its cardiac function. Some clinicians use a scale of 1 to 6 and some people use a scale from 1 to 5. Either way, by the time the dog is down to 50% cardiac function it’s in pretty sorry shape.

The top ‘grade’ of heart murmur is “when you can literally feel the rushing of the murmur with your fingertips through the chest wall.”

The number one cause of heart murmurs in dogs is germs from the mouth.

The number one reason heart murmurs get worse is more and continued germs from the mouth.

When a heart murmur shows up in an old dog, I don’t get very excited. Many times it shows up when the dog is 11+ years old and the owner has given up on the teeth for fear of losing the dog under anesthesia*.

*I’ve never lost a dog under anesthesia.

In large breed dogs a heart murmur speaks to a drastically shortened life. In small breed dogs, it starts a three year countdown. On average.

It could be said that every dog with a heart murmur has four years to live, minus one year for each 25 pounds it weighs.

A dog under 25 pounds with a heart murmur will very likely live three years depending on the severity and how fast it progresses.

Factors influencing how fast a murmur ends a SMALL dog:

  1. Age of dog at time of diagnosis
  2. Severity of murmur when found
  3. Speed at which it goes up in grade
  4. Weight of the dog
  5. Degree of dental disease during progression
Heart Murmurs in Dogs

Heart Murmurs in Dogs are a short term problem for large dogs.

As you can see, subtracting a year for every 25 pounds a dog weighs means that a dog that weighs 100 pounds is unlikely to make it one year.
A large breed dog that is quite overweight, that gets a heart murmur in it’s later years is (usually) not destined to last long.

Heart Murmurs in Dogs

A heart murmur that shows up in a dog under eight years old should be promptly evaluated by a specialist with what is called an echocardiogram. They look at the heart with an ultrasound machine and take measurements, to keep track of the progression, and they can tell you whether or not that heart murmur will be a story-ender or something the dog can live with, even, something the dog was born with.

The number one cause of heart murmurs in dogs is germs from the mouth.

Another prognostic feature of heart murmurs is how fast they progress. If a heart murmur takes a year to worsen by one grade level, that’s pretty normal. But if a heart murmur goes from a grade one to a grade 5 in one or two years, it might be a good idea to intervene.

If money grew on trees, all heart murmurs would be assessed by echocardiogram in the event that antibiotics, or blood pressure medicines or even calcium channel blocker‘s might slow down the progression

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Dr Erik Johnson

Dr Erik Johnson is a Marietta, Georgia Veterinarian with a practice in small animal medicine. He graduated from University of Georgia with his Doctorate in 1991. Dr Johnson is the author of several texts on Koi and Pond Fish Health and Disease as well as numerous articles on dog and cat health topics.