🫀 Understanding Heart Murmurs in Dogs and Cats: A Vet's Guide for 2025 🐾

By Dr Duncan Houston, BVSc

When your vet mentions a heart murmur during a routine check-up, it can feel alarming. But don’t panic — not all murmurs are a cause for immediate concern. As a veterinarian, I often hear the same questions from loving pet parents: “What does this murmur mean? Does it mean heart disease? Will my pet be okay?” Let’s dive into the details of heart murmurs in both dogs and cats to help you better understand the sounds coming from your furry companion’s heart. ❤️🐶🐱

🔊 What Is a Heart Murmur?

Normally, when we listen to a pet’s heart with a stethoscope, we hear two distinct sounds: "lub-dub…lub-dub". These are the sounds of the heart valves opening and closing. A heart murmur is an extra or unusual sound heard between the “lub” and the “dub.” It often sounds like a “whoosh” or “shoosh” — like water flowing over rocks. 🌊

This “whooshing” represents turbulent blood flow. Instead of blood flowing smoothly, something is disturbing it — much like rapids in a river. 🏞️

💡 What Causes Heart Murmurs?

There are many reasons why turbulent blood flow might occur inside your pet’s heart. Some of the common causes include:

• Leaky heart valves – the most common cause in dogs, especially the mitral valve
• Valve stenosis – narrowed valves or blood vessels forcing blood through a tight opening
• Septal defects – holes between heart chambers (usually congenital)
• Excitement or stress – especially in cats or puppies, causing temporary murmurs
• Low blood viscosity (anemia) – making blood flow more turbulent
• Vibrating heart structures – similar to plucked guitar strings, causing vibration noises

To understand murmur origins, it helps to know your pet’s heart has four chambers — two atria and two ventricles — and four main valves: mitral, tricuspid, aortic, and pulmonic. When any of these valves don’t function properly, turbulence can result. 🫀

🔬 Are There Different Types of Murmurs?

Yes! Murmurs are classified by:

• Timing – when they occur in the heartbeat (systolic, diastolic, or continuous)
• Location – where they are heard on the chest (left, right, upper, lower)
• Quality – their tone, shape, and pitch

For example:

• Murmurs heard on the lower left chest in older dogs often suggest degenerative mitral valve disease 🐕
• Continuous murmurs in the left armpit may suggest a patent ductus arteriosus (PDA) 🧬
• Loud right-sided murmurs may be caused by ventricular septal defects or tricuspid valve leaks

But in cats, identifying the cause from sound alone is much harder. A soft murmur might be totally innocent — or a sign of serious heart disease. That’s why diagnostic imaging is crucial. 🐈

🟢 Benign or “Innocent” Murmurs

Some murmurs are harmless and don't reflect heart disease. These benign murmurs are common in:

• Puppies – often soft and disappear by 12–15 weeks 🐾
• Cats – may have benign murmurs even into adulthood 🐱
• Pets with anemia or excitement-related murmurs

🧬 Congenital vs. Acquired Murmurs

Congenital murmurs are present from birth and usually linked to structural heart defects. These often require early diagnosis and treatment. 🍼

Acquired murmurs develop later in life and may or may not be linked to disease. Older dogs are more likely to develop murmurs due to degenerative changes. 🧓🐕

📊 What Does a Murmur Grade Mean?

Vets use a scale from 1 to 6 to describe murmur intensity:

• Grade 1: Very soft, often hard to detect
• Grade 2: Soft but audible
• Grade 3: Moderately loud, often consistent
• Grade 4: Loud and easily heard
• Grade 5: Loud with a “thrill” felt on the chest wall
• Grade 6: Extremely loud, even heard without a stethoscope in quiet conditions

Note: A higher grade doesn’t always mean a more serious problem! Some mild valve defects can create loud murmurs, while severe disease may produce softer ones. 🎧

🐶 What To Do if Your Dog Has a Murmur

In dogs, many murmurs can be diagnosed based on:

• Breed (e.g., Cavaliers often develop mitral valve disease)
• Age and symptoms (e.g., coughing, exercise intolerance)
• Physical exam findings

Your vet may recommend:

• Monitoring over time with regular check-ups
• Imaging such as echocardiograms or chest X-rays
• Referral to a veterinary cardiologist

For breeding dogs, a murmur could indicate a genetic issue. In these cases, full evaluation or sterilization may be advised. 🧬

🐱 What To Do if Your Cat Has a Murmur

In cats, diagnosing a murmur’s cause is more complex. Even benign murmurs can sound identical to those caused by dangerous conditions like hypertrophic cardiomyopathy. Only an echocardiogram can confirm the cause. 🧪

💊 How Are Murmurs Treated?

The murmur itself isn’t treated. Treatment depends on the underlying cause. For example:

• Mitral valve disease may require medications like pimobendan and ACE inhibitors
• Congenital defects may need surgery
• Anemia-induced murmurs are resolved by treating the anemia

Some pets may live comfortably for years without intervention, while others need close monitoring and medical support. 🎯

🧘 Final Thoughts from Dr Duncan Houston

If your vet tells you your pet has a murmur, don’t panic. Instead, work closely with your veterinary team. A murmur is simply a clue — and with the right diagnostics and care, many pets live long, happy lives. 💞

And remember, if you ever need trusted support or guidance on your pet’s health journey, the team at AskAVet.com is here to help! You can even download the Ask A Vet App 📱 for 24/7 access to licensed veterinary professionals. 🐾