Hearing that your dog has a heart murmur, or that your cat’s vet picked one up during a check-up, can be worrying. A heart murmur is simply an abnormal sound in the heartbeat, and while it always deserves a proper look, it doesn’t automatically mean something serious is wrong. This guide explains what a heart murmur is, what causes it in dogs and cats, and what happens next.
What Is a Heart Murmur?
A healthy heartbeat makes a steady “lub-dub” sound as blood moves through its four chambers. A heart murmur is an extra sound, often described as a whooshing or swishing noise, caused by turbulent blood flow within the heart. Murmurs are usually picked up when a vet listens to your pet’s heart with a stethoscope during a routine check-up, so many pets are diagnosed before they ever show signs of illness.
What Causes a Heart Murmur?
Heart murmurs can come from a few different places, and not all of them involve heart disease.
Structural causes affect the heart itself. These include:
- Congenital defects your pet was born with, such as a hole between heart chambers or a narrowed valve
- Acquired conditions that develop later in life, most commonly mitral valve disease in older small-breed dogs, or thickened heart muscle (cardiomyopathy) in cats
Extracardiac causes don’t involve the heart at all, but still create turbulent blood flow. These include:
- Anaemia, or low red blood cell count
- Fever or infection
- Pregnancy
- Obesity
- Stress or a fast heart rate at the time of examination
This is why a heart murmur on its own isn’t a diagnosis. It’s a sign that something is affecting blood flow, and working out what that is comes next.
Heart Murmur Grades: What Grade I to VI Means
Vets grade heart murmurs on a scale from I to VI based on how loud they are.
- Grade I to II: Very soft, often only heard in one spot and easy to miss
- Grade III to IV: Easily heard, and audible on both sides of the chest
- Grade V to VI: Very loud, and can sometimes be felt through the chest wall
It’s important to know that the grade reflects loudness, not severity. A loud murmur isn’t always a sign of serious disease, and a soft murmur can sometimes accompany a more significant problem. The grade is one piece of the picture, not the full diagnosis.
Heart Murmur Symptoms in Dogs
Many dogs with a heart murmur show no symptoms at all, especially in the early stages. When symptoms are present, they can include:
- Coughing
- Tiring more easily during walks or play
- Laboured or rapid breathing, particularly at rest
- Pale or bluish gums
- Weakness, collapse, or fainting
- Reduced appetite or weight loss
If your dog is showing any of these signs alongside a known or suspected murmur, it’s worth booking a check-up promptly rather than waiting.
Heart Murmur Symptoms in Cats
Cats are harder to read than dogs when it comes to heart problems. Many cats with a heart murmur show no outward symptoms until the underlying condition has progressed, which is why routine check-ups matter even when a cat seems perfectly well. When symptoms do appear, they can include:
- Laboured or open-mouth breathing
- Lethargy or hiding more than usual
- Reduced appetite
- Sudden weakness or collapse
Because cats mask illness so well, a heart murmur picked up during a routine exam is often the first and only warning sign before symptoms develop.
Innocent Murmurs in Puppies and Kittens
Not every murmur points to a problem. Young, fast-growing puppies and kittens can develop what’s called an innocent or physiologic murmur, usually soft (Grade I to II) and with no other symptoms. These are common, aren’t harmful, and typically resolve on their own by around four to five months of age. Your vet will usually recommend a follow-up check to confirm the murmur has faded rather than treating it straight away.
How Vets Diagnose a Heart Murmur
Once a murmur is detected, the next step is finding out what’s causing it. Common diagnostic tools include:
- X-rays, to check the size and shape of the heart
- An electrocardiogram (ECG), to check heart rhythm
- Blood tests, to rule out causes like anaemia or infection
- An echocardiogram, an ultrasound of the heart that gives the clearest picture of what’s actually happening inside it
An echocardiogram is considered the gold standard for getting to the bottom of a heart murmur, since it lets our vets see the heart’s structure and blood flow directly.
Heart Murmur Treatment for Dogs and Cats
Treatment depends entirely on what’s causing the murmur, not the murmur itself.
- Innocent murmurs in young pets usually need no treatment beyond a follow-up check
- Murmurs caused by anaemia, infection, or other extracardiac issues often improve once the underlying cause is treated
- Murmurs linked to heart disease may be managed with medication, diet changes, and regular monitoring
- Some congenital defects can be corrected surgically
Your vet will recommend a plan based on your pet’s specific diagnosis, age, and overall health.
Outlook and Prognosis
The outlook for a pet with a heart murmur depends on its cause, not its grade or loudness. Innocent murmurs carry an excellent outlook and often resolve without treatment. Murmurs linked to a treatable cause, like anaemia, often improve once that condition is managed. Murmurs linked to ongoing heart disease vary more, but many dogs and cats live comfortably for years with the right monitoring and care.
Frequently Asked Questions
Is a heart murmur painful for my pet?
No. A heart murmur itself doesn’t cause pain. Any discomfort would come from an underlying condition, not the murmur sound itself.
Can a heart murmur go away on its own?
Sometimes. Innocent murmurs in puppies and kittens often resolve by four to five months of age. Murmurs linked to a treatable cause can also improve once that cause is addressed.
Is it safe to put my pet under anaesthesia if they have a heart murmur?
This depends on the cause and severity of the murmur. Your vet will assess your pet beforehand and may recommend extra monitoring during anaesthesia if needed.
Will my pet need a heart murmur checked regularly?
Yes, in most cases. Even mild or innocent murmurs are usually monitored over time to make sure nothing changes.
Book a Heart Health Check-Up at Plus One Vet Sunnybank
If your dog or cat has been diagnosed with a heart murmur, our team at Plus One Vet Sunnybank can help you understand what it means and what to do next. Book a check-up today.
