Heart murmur grades in dogs: what grade 3 or 4 really means

Let me guess. It was supposed to be a routine checkup. Your dog was mostly concerned with where the treats went, and then your vet said the word "murmur," with a number attached: grade 3. And now you're home looking up heart murmur grades in dogs, trying to work out whether a 3 is good news or bad news.

Take a breath. Let's walk through it the way I would if you were sitting across from me.

First, what a murmur actually is

When blood swirls through the heart instead of flowing smoothly, it makes an extra whooshing sound I can hear with a stethoscope. That whoosh is the murmur.

Here's the thing: a murmur is a clue, not a diagnosis. It tells me something is stirring up the blood flow, not what. It could be a leaky valve, a weak heart muscle, a problem a puppy was born with, or something outside the heart, like anemia (a low red blood cell count).

You can't hear it at home, by the way. Your ear on his chest just gets you a heartbeat and a confused dog.

Heart murmur grades in dogs, in plain words

Vets grade a murmur by how loud it is, from 1 to 6. On your paperwork, "3/6" just means grade 3 out of 6.

• Grade 1: very faint. I need a quiet room to hear it.
• Grade 2: soft, but easy to hear, in one small spot.
• Grade 3: medium loud. I hear it the second the stethoscope lands in the right place.
• Grade 4: loud right away, but I can't feel it with my hand yet.
• Grade 5: very loud, and I can feel a buzz through the chest wall with my hand.
• Grade 6: so loud I can still hear it with the stethoscope lifted just off the chest.

Grading is a judgment call (some charts even stop at 5). One vet's 3 is another vet's 4, so don't get hung up on the exact number.

The grade isn't the same as how sick the heart is

This is the part I most want you to hear: the grade is how loud the murmur is, not how sick the heart is.

A soft murmur, grade 1 or 2, usually means no heart disease or a mild problem. A very loud one often goes with more serious disease. So if you're asking about a grade 3 heart murmur in dogs: the middle grades, 3 and 4, don't tell me on their own how bad things are. A grade 3 can belong to a dog who'll cruise along for years, or to one whose heart has already started to enlarge.

Next, most people look up life expectancy. The grade can't answer that. What's going on inside the heart can, and your vet can tell you where your dog sits after a closer look. The good news: with a leaky valve, the most common cause, the murmur usually shows up years before any heart failure does, and only about 3 in 10 of those dogs go on to develop heart failure.

I know "heart failure" sounds like the heart is about to stop. It isn't. It means the heart can't keep up, and fluid starts backing up into the lungs. The counting below helps catch that early.

Why your dog has one: the usual suspects

A small, older dog. The usual cause is a leaky mitral valve (the vet name is myxomatous mitral valve disease). It's the most common heart disease in dogs, about 75% of cases, mostly in smaller, older dogs. Cavalier King Charles Spaniels are famous for it. The valve stops sealing, so a little blood leaks backward with every beat. That's the whoosh.

A big dog. In large breeds like Dobermans, Boxers and Great Danes, I also think about a weak, stretched heart muscle (the vet name is dilated cardiomyopathy), usually from middle age on. It can go a long time with no signs and only a soft murmur, so a big dog's soft murmur can be worth a closer look.

A puppy. Lots of puppies have a soft murmur that isn't heart disease at all. These innocent murmurs are mostly outgrown by about 6 months. I listen again at the next puppy visits. If it's loud, or still there past that age, I want a closer look, because some puppies are born with a heart problem.

What comes next: X-rays and a heart ultrasound

Chest X-rays show how big the heart is and whether there's fluid in the lungs.

An echocardiogram is an ultrasound of the heart. It's the best test for finding the cause: which valve, how big the leak is, how well the muscle squeezes. Getting one may mean a trip to a veterinary cardiologist.

Some vets also use a heart blood test called proBNP, and a blood pressure check is a good idea too.

Which one first? It depends on the dog, what I'm hearing, and what works for your household. I usually start with chest X-rays, then an echo if the heart looks enlarged or questions remain. Not every vet does it in that order, and there's no wrong way here.

The stages, and when medicine starts

For the leaky valve, most vets follow a set of staging guidelines. The stage, not the grade, decides treatment.

• Stage A: no heart disease yet, but a breed at higher risk.
• Stage B1: a leaky valve, but the heart isn't enlarged. No medicine is recommended yet, just a recheck, usually in 6 to 12 months.
• Stage B2: the heart has enlarged from the leak, but your dog still feels fine. Here the guidelines recommend starting a heart medicine called pimobendan (you may see it as Vetmedin) to help delay heart failure. A murmur of grade 3 or louder is one clue to this stage, along with X-ray and echo measurements.
• Stage C: heart failure now, or in the past. That usually means a few medicines, often including a water pill to keep fluid off the lungs.
• Stage D: heart failure that's hard to control with standard treatment.

So here's what "grade 3 or 4" really means: let's find out what stage we're in. A grade 3 in a B1 dog means rechecks and watching. A grade 3 in a B2 dog may mean starting medicine now. Same grade, different plan.

Between medicines, rechecks and breath counts, there's a lot to keep straight. Honestly, that's why I built WagNote (full disclosure: it's my app). I kept seeing owners of dogs with heart disease struggle to keep track of everything, so I put it all in one place.

The number I want you to know: sleeping breaths

When fluid starts backing up into the lungs, your dog breathes faster, and you'll see it best while he's asleep. A rise above his own normal sleeping rate is the best early warning we have.

Wait until he's sound asleep, count each rise and fall of his chest as one breath for 30 seconds, and double it. Write it down with the date on a sheet taped to the fridge, or just tap it into WagNote's breath counter and it does the math and keeps the chart.

What's normal? A sleeping dog typically sits around 15 to 20 breaths a minute, and anything under 30 is normal. Above that, vets differ. Most cardiology handouts draw the line at about 30, and some clinics use 35. Typically, I say 40, but that's a vet call. I also watch for a jump from his own normal: if he usually sleeps at 15 to 20 and now he's at 35, that might be a problem. So ask your vet, "What number should I call you about?"

How often? If he isn't on heart medicine yet, ask your vet whether to start counting now. Once he's on heart medicine, count at night, every night, and in active heart failure your vet may want counts several times a day. More on counting, and on high numbers, in the 30-second sleeping breath check.

Next to the counts, jot down any coughing (especially at night), tiring sooner on walks, restless nights, or eating less, or add it as a note in WagNote, and bring it all to every recheck (what to bring to the vet has more).

When to worry, and when it can't wait

Most murmurs are a "book a visit and look closer" problem, not an emergency. But go to your vet or an emergency clinic right away if your dog is working hard to breathe, is breathing fast while resting and can't settle or lie down, has pale, gray or blue gums, or faints or collapses. Don't wait for morning on those.

If you do one thing this week: call your vet and ask, "What stage is his heart in, and should I be counting his sleeping breaths?" If it's yes, write each count down, or tap it into WagNote. Your vet will love you for it.