My dog/cat has a heart murmur – now what?

When you bring your pet to the veterinarian, you want everything to go well, your pet to be happy, and your vet to find nothing abnormal on physical exam. So when the veterinarian tells you that your dog or cat has a heart murmur, it can be a bit of a shock. Often these animals have shown no symptoms, so the diagnosis seems to come out of left field, and can be distressing.

What is a heart murmur anyway? Think back to high school biology, when you learned that the (normal) heart makes a sound like “lub dub.” It’s two distinct beats, often in a nice rhythm. Hearts with a murmur do not have two clear, crisp beats. Depending on the nature of the murmur, there can be a wide range of sounds. In severe cases, the whole “lub dub” may be obliterated, and the heart just sounds like a machine motor. In most cases, either the lub, the dub, or both is obscured, so instead of two distinct beats, it’s garbled…like if you were singing the words “lub dub,” and you were underwater.

So what now? Your vet has heard this murmur, this heart abnormality, and you’re a little shocked. Your vet might then tell you the murmur has a grade. We typically assign them a grade on a scale of 1-6, based on severity, with 1 being most mild, and 6 being most severe. And when we write heart murmurs in the records, we use Roman numerals… because we vets are just so schmancy. So a grade 3 out of 6 heart murmur would be a Grade III/ VI murmur. (See how I did that?)

Here’s what I tell my clients after I find a heart murmur on physical exam:

With cats, I’ve learned that the grade of the heart murmur does not necessarily correlate to the severity of the disease. I have had cats with Grade 5 (or Grade V/VI) murmurs, who never have any clinical problems. They’ve lived long, fulfilling lives. I’ve even spayed and neutered cats with horrible-sounding heart murmurs, and the anesthesia was rather uneventful (I was sweating bullets, but the cat did fine). On the other hand, I have had cats suddenly die from cardiomyopathy who never had a heart murmur. Ever. The most common kind of heart disease in cats, hypertrophic cardiomyopathy (HCM), may or may not present with a murmur. So with cats and heart murmurs, I respect it, but I don’t get so stressed out.

Dogs are a little more straight-forward. If a dog has a heart murmur, in my experience, the worse the murmur, the more severe the heart disease. (Of course, there are always exceptions to this rule as well.) Where we hear the murmur on a dog can tell us a lot. In older dogs, especially small/medium breeds, we’ll commonly hear the murmur on the left side of the chest. This is where the mitral valve lives, and mitral valve insufficiency is perhaps the most common cause of heart disease in older dogs. If the murmur is on the right side of the heart, that’s where the tricuspid valve lives. This right side is also the area where heartworms live, so a dog with heartworm may have a murmur loudest on this side. (There are many other diseases and maladies that can cause heart murmurs in these locales, I’m just giving examples of the most common.)

Cavalier King Charles Spaniels are the heart murmur poster child!

Of course, with both species, the age of the animal is a huge factor. If it’s a young puppy or kitten, then the heart murmur is likely a birth defect, and should be taken seriously. There are a handful of heart murmurs that these young kiddos can outgrow, so cross your fingers. In older animals who have had normal-sounding hearts their whole lives, it’s usually valve disease or other cardiomyopathy.

Whenever we first diagnose a murmur, we vets always ask if the animal has had any symptoms: coughing, panting more (or panting at all in a cat!), having to stop playing to catch her breath, weight loss, etc. Most owners say no. If there are no symptoms, we’ll have a couple options. One is to do nothing now and monitor exercise and breathing. My favorite tool to monitor for heart disease is the resting respiratory rate. It’s easy, and it’s free! You simply count how many times your pet breathes per minute. Yes, it takes practice, and you’ll get some crazy numbers in the beginning. A lot of research has gone into the statistics, actually, and if the pet breathes more than 35 breaths per minute, there is a high likelihood heart failure is starting. Of course, this is resting breaths…one of my clients calls it “sleep breathing.” So you do this when the dog or cat is relaxed, and hasn’t just finished playing. (I’ll soon have a video demonstrating how to count these breaths.)

A more aggressive, better option is to get x-rays of the chest. I pursue this more in dogs than cats. Why? Cats make nothing easy for us. Ever. I had one cat that was breathing horribly, and was able to get it on oxygen and stable, then get some x-rays. Cat chest x-rays are notoriously hard to read, so I sent them off for a specialist to read. The radiologist diagnosed the cat with asthma, so we started treating for asthma. I referred the cat to a 24/7 specialty center for hospitalization, and they happened to have a cardiologist. That specialist looked at the very same x-rays and diagnosed heart failure. My point? If two people who are freakin’ specialists at this stuff can’t even agree on a cat chest x-ray…I give up. (And to boot, you treat feline asthma and heart failure very different ways!).

Dogs are much more straightforward. Chest x-rays on dogs often reveal heart failure quite well. When we take an x-ray, we are looking at the shape of the heart. Is there a chamber, like the left atrium, that’s bigger than it should be? Are the blood vessels in the lungs extra big? Is there fluid in the lungs? This is all helpful information.

The next diagnostic step, depending on the severity of the x-rays, could be an echocardiogram. This is an ultrasound of the heart, and it gives us much more detailed information about how well the valves are moving, how much the heart muscle is contracting, and if blood is swirling in circles instead of moving in the direction it’s supposed to. With cats, I will often skip the x-rays and have them go straight to this step if I am concerned. With dogs, I’ll do x-rays first to see what we’re up against. An echocardiogram is rather expensive ($350-$800), and often requires a trip to a specialist, so it’s not something many pet owners are rushing to do in a pet with no symptoms.

So bottom line, hearing your pet has a heart murmur can be a shock, and can be sad. But detecting the disease early is a good thing, because you can intervene if necessary! The point of this article is not to be an explanation of all types of heart disease, but to give pet owners who are shocked at this new finding in their pet some hope, an explanation, and a plan. I’ll have detailed articles about specific cardiac diseases soon!

Posted in General health, Senior pets.


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