First off, here’s a general list of signs of heart failure in dogs:
- A hacking cough
- Increased breathing rate at rest
- Labored breathing
- Lack of energy
- Inability to exercise
- Blue-tinged or pale gums
Now, not so many years ago, the parent of a happy, healthy dog with a loud heart murmur would be advised by their vet to wait and only start treatment once signs of heart failure developed. This was accepted wisdom.
Back then, we all believed starting drugs too early, before the dog developed a cough or struggled to exercise, would reduce the medication’s effectiveness when the dog really needed it. But this advice has changed.
Vets now know that a certain drug, when given early (before clinical signs develop), markedly extends the life expectancy of dogs with Grade 3 murmurs that are due to leaky heart valves.
Today’s veterinary world relies on “evidence-based medicine” (EBM). This isn’t the sort of evidence where the vet once had a patient with X terminal disease and gave drug Y, and the dog made a full recovery. No, this isn’t about personal experience but instead repeatable scientific fact.
The evidence has to be solid and factual, with a statistical analysis that stands up to scrutiny and has irrefutable results. And the EPIC study into the treatment of heart murmurs has all of this (see references 1 and 2 at the end for more detail).
The name of the drug in question is pimobendan (Vetmedin™). In truth, pimobendan has been around for years; indeed, your dog may already be on it. But what’s different is the timing of when the drug is started.
Vets now have real, hard evidence that starting pimobendan early in at-risk dogs has big benefits. These include:
- 1/3 reduction in the likelihood of developing heart failure at any given time (when compared with similar dogs not on any treatment)
- 15 months more good-quality life than similar dogs not receiving pimobendan
Indeed, the benefits to canines with wonky hearts were so marked that the clinical trial had to be halted ahead of time. It became clear that the dogs in the control group (those not receiving a sugar pill) were becoming sick sooner and living less than those on pimobendan. On ethical grounds, it simply wasn’t fair to withhold a beneficial drug once the truth was recognized, and the placebo group were wised up.
Pimobendan and Your Dog
At vaccination, the vet finds the dog has a heart murmur, but they’re fit and well, so they should start pimobendan, right?
Unfortunately, things are more complicated than that.
OK, this is where a bit of science comes in. First, there’s a big difference between having a heart murmur and heart failure:
- Heart murmur: A murmur refers to the noise made when some blood leaks in the wrong direction through a heart valve.
- Murmurs vary from mild (Grade 1) to severe (Grade 6).
- Some murmurs stay the same for the duration of the dog’s life, some go away and others get worse with time.
- Heart failure: This happens when the heart fails as a pump and can’t push enough blood around the body. Heart failure can be controlled (for a while) with drugs, but it can’t be cured.
The trick is to work out which group the dog belongs to. This requires a bit of wizardry with a cardiac ultrasound scan that looks for heart enlargement. This is because there’s a sweet spot where the dog shows physical changes in the shape of the heart but they’re still fit and well. This is the dog who will benefit from taking pimobendan early.
Right now, your heart might be sinking — you don’t want your dog to have tests.
Don’t panic. Dogs with soft murmurs (Grades 1 and 2) can sit tight and wait some more. These dogs are exceedingly unlikely to have heart enlargement. Quite simply, their hearts are still very fit.
However, if a vet hears a Grade 3 murmur, they will sit up and take notice.
Heart Murmur Grades
The vet listens with a stethoscope to the dog’s chest.
- Grade 1: The softest murmur — so quiet it takes minutes of careful listening in a quiet room to detect it
- Grade 2: A soft murmur heard without difficulty
- Grade 3: Low to moderate noise
- Grade 4: Moderate to loud noise
- Grade 5: Loud noise that makes the chest wall vibrate
- Grade 6: So loud that the murmur is heard with the stethoscope not directly against the chest wall
Grade 3 dogs are those most likely to be well but teetering on the edge of becoming sick. A heart scan allows the vet to take measurements of the heart’s size, which can catch the dog before heart failure starts.
So the dog with a quiet murmur should have a vet listen to their chest every 6–12 months to detect any changes. For dogs who are outwardly well but have a Grade 3 murmur, imaging will detect signs of wear and tear.
Then you can decide on starting pimobendan, a drug that could reduce the risk of heart failure by 1/3 and increase life expectancy by 15 months.
This vet explains the ins and outs of heart murmurs in dogs:
In truth, the major downside is cost. Heart scans are expensive, and the drug itself isn’t cheap. Thus, several years of an expensive heart med can total up to a tidy sum.
And finally, even with pimobendan, a few dogs will defy the odds and not do so well. Such is the law of averages and the pitfall of statistics. But with pimobendan, there is new hope.
This pet health content was written by a veterinarian, Dr. Pippa Elliott, BVMS, MRCVS. It was last reviewed Jan. 26, 2018.
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