Heart Murmurs Explained
If you own a Cavalier King Charles Spaniel, there's a good chance you've heard the term heart murmur. It can be an alarming phrase, particularly when your veterinarian mentions hearing one during a routine health check.
The important thing to remember is that a heart murmur is not a diagnosis—it is a clinical finding. It is an abnormal sound heard through a stethoscope that indicates blood is flowing turbulently through the heart. While some murmurs are harmless, others may indicate underlying heart disease that requires further investigation.
Because Cavalier King Charles Spaniels are predisposed to myxomatous mitral valve disease (MMVD), regular heart examinations are an essential part of lifelong healthcare. Early detection allows veterinarians to monitor disease progression and determine when treatment may be beneficial.
What Is a Heart Murmur?
A normal heartbeat produces the familiar "lub-dub" sound as the heart valves close.
A heart murmur is an additional sound, often described as a whooshing, swishing or blowing noise, caused by turbulent blood flow within the heart or major blood vessels.
A murmur itself is not a disease. Instead, it is a sign that prompts your veterinarian to investigate why the blood flow has become turbulent.
What Causes a Heart Murmur?
Heart murmurs can have several different causes.
These include:
Leakage through a heart valve.
Congenital (present at birth) heart defects.
Narrowing of blood vessels or valves.
High blood flow states.
Occasionally, harmless ("innocent" or physiological) murmurs.
In adult Cavalier King Charles Spaniels, the most common cause of a heart murmur is myxomatous mitral valve disease (MMVD), a condition in which the mitral valve gradually degenerates and no longer closes properly, allowing blood to leak backwards into the left atrium.
Why Are Cavaliers More Prone to Heart Murmurs?
The Cavalier King Charles Spaniel has a well-recognised inherited predisposition to MMVD.
This means Cavaliers are more likely than many other breeds to develop changes in the mitral valve during their lifetime.
Importantly, not every Cavalier will develop significant heart disease at the same age or progress at the same rate. Responsible breeding programs aim to reduce the impact of this disease by following recommended cardiac screening protocols and making informed breeding decisions.
How Is a Heart Murmur Detected?
Most heart murmurs are first detected during a routine physical examination.
Using a stethoscope, your veterinarian listens carefully to the heart from several positions on the chest.
If a murmur is heard, they will assess:
Where it is heard most clearly.
When it occurs during the heartbeat.
How loud it is.
It is overall character.
Although auscultation (listening with a stethoscope) is an excellent screening tool, it cannot determine the exact cause of a murmur. Additional testing is often recommended.
Understanding Heart Murmur Grades
Heart murmurs are graded on a scale from Grade I to Grade VI according to how loud they sound through a stethoscope.
GradeDescriptionGrade IVery soft and difficult to hear.Grade IISoft but consistently audible.Grade IIIModerately loud.Grade IVLoud and easily heard.Grade VVery loud with a vibration (thrill) felt through the chest wall.Grade VIExtremely loud and audible even when the stethoscope is lifted slightly from the chest.
One important point is that the grade of a murmur does not always reflect the severity of the underlying heart disease. A louder murmur does not necessarily mean the disease is more advanced, and a soft murmur should never be ignored.
Does a Heart Murmur Mean My Dog Has Heart Failure?
No.
This is one of the most common misconceptions.
Many dogs with heart murmurs have no clinical signs and continue to live happy, active lives for years.
Heart failure occurs only if heart disease progresses to the point where the heart can no longer pump blood efficiently enough to meet the body's needs.
Regular monitoring allows veterinarians to identify changes well before heart failure develops.
What Tests Might Be Recommended?
If your veterinarian detects a heart murmur, they may recommend further investigations, particularly if the murmur is new or increasing in intensity.
These may include:
Echocardiography (heart ultrasound).
Chest radiographs (X-rays).
Electrocardiogram (ECG) if indicated.
Blood pressure measurement.
Blood tests where appropriate.
An echocardiogram performed by a veterinary cardiologist is considered the best way to assess heart structure and function.
Should My Cavalier See a Veterinary Cardiologist?
Many Cavaliers with newly diagnosed murmurs benefit from referral to a veterinary cardiologist.
A cardiologist can:
Confirm the cause of the murmur.
Determine the stage of heart disease.
Assess whether treatment is indicated.
Develop an ongoing monitoring plan.
Early assessment provides valuable baseline information that can guide future care.
Signs Owners Should Watch For
Many Cavaliers with early MMVD show no outward signs.
As disease progresses, owners may notice:
Reduced exercise tolerance.
Increased sleeping.
Coughing.
Rapid or laboured breathing.
Breathlessness.
Reduced appetite.
Episodes of weakness or collapse.
These signs do not always indicate heart disease, but they should always be assessed promptly by a veterinarian.
Can Heart Murmurs Be Prevented?
Not always.
Because MMVD has a strong inherited component, responsible breeding is one of the most important ways of reducing its impact within the breed.
Owners can also support lifelong heart health by:
Choosing a puppy from health-tested parents.
Attending regular veterinary examinations.
Maintaining a healthy body weight.
Feeding a balanced diet.
Providing appropriate exercise.
Following veterinary advice regarding ongoing monitoring.
Frequently Asked Questions
What is a heart murmur?
A heart murmur is an abnormal sound caused by turbulent blood flow within the heart. It is a clinical finding rather than a disease itself.
Does every heart murmur mean my Cavalier has mitral valve disease?
No. Although MMVD is the most common cause of heart murmurs in adult Cavaliers, other conditions can also cause murmurs. Your veterinarian may recommend further testing to determine the cause.
Can a dog have a heart murmur without showing symptoms?
Yes. Many dogs with early-stage heart disease appear completely healthy and show no outward signs for months or even years.
Is a Grade VI murmur always worse than a Grade II murmur?
Not necessarily. Murmur grade reflects how loud the murmur sounds, not always the severity of the underlying disease.
How often should my Cavalier's heart be checked?
Every Cavalier should have their heart examined during routine veterinary visits. As dogs age, or if a murmur is detected, your veterinarian may recommend more frequent examinations or referral to a veterinary cardiologist.
Can dogs with heart murmurs still live happy lives?
Absolutely. Many Cavaliers diagnosed with a heart murmur continue to enjoy excellent quality of life for many years with appropriate monitoring and, when necessary, medical treatment.
Learn More
Continue exploring the Cavalier Knowledge Library:
Cardiac Screening for Cavaliers
Senior Cavalier Care
A heart murmur can be worrying to hear, but it is not a reason to panic. It is an important clue that allows veterinarians to investigate your dog's heart health and provide appropriate care. With regular veterinary examinations, responsible breeding practices and advances in veterinary cardiology, many Cavalier King Charles Spaniels with heart murmurs continue to live active, happy and rewarding lives alongside the families who love them.
References
Keene, B. W., Atkins, C. E., Bonagura, J. D., et al. (2019). ACVIM Consensus Guidelines for the Diagnosis and Treatment of Myxomatous Mitral Valve Disease in Dogs. Journal of Veterinary Internal Medicine, 33(3), 1127–1140.
American College of Veterinary Internal Medicine (ACVIM). Consensus Guidelines for the Diagnosis and Treatment of Myxomatous Mitral Valve Disease in Dogs.
American College of Veterinary Internal Medicine. ACVIM Staging System for Myxomatous Mitral Valve Disease.
PetMD. Heart Murmurs in Dogs. Reviewed by veterinarians.
Häggström, J., Boswood, A., & O'Grady, M. (Referenced within the ACVIM Consensus Guidelines). Research into myxomatous mitral valve disease and Cavalier King Charles Spaniels.
Disclaimer
The information provided in the Cavalier Knowledge Centre is intended for general educational purposes only and is not a substitute for veterinary advice, diagnosis or treatment.