Hearing that your dog or cat has a heart murmur can be concerning, especially if you are not sure what it means or what comes next. Many pet owners leave their veterinary visits without a clear understanding of what they were told, or a discussion about how serious their pet's condition is and whether they need additional care.
In this blog, we will explore heart murmurs in pets to address your questions. We'll explain what a heart murmur is, what it may indicate, and how veterinarians evaluate heart murmurs in dogs and cats, helping you better understand your pet's health.
What a Heart Murmur Means in Dogs and Cats
A normal heartbeat produces a consistent sound as the heart valves close and blood moves through the chambers of the heart. A murmur is an additional sound layered on top of that rhythm, often described as a soft swishing or whooshing noise.
This sound develops when blood flow becomes turbulent rather than smooth. Turbulence can result from structural heart disease, changes in the heart valves, or congenital conditions present at birth. In some cases, conditions outside of the heart, such as anemia or fever, may also contribute to the presence of a murmur.
It's important to understand that a heart murmur is not a diagnosis on its own, but it can be an important clinical finding that helps guide your veterinarian’s next steps. Because of this, a heart murmur should always be interpreted within the context of the full physical exam and your pet’s overall health, rather than viewed as a condition on its own.
How Veterinarians Classify Heart Murmurs
When a murmur is detected, your veterinarian will evaluate several characteristics beyond its presence. These include when the murmur occurs during the heartbeat, where it is heard most clearly, and how intense it is.
Most murmurs in dogs and cats are systolic, meaning they occur when the heart contracts. Diastolic murmurs occur when the heart relaxes between beats, while continuous murmurs are present throughout the cardiac cycle. The timing of a murmur can help narrow the list of possible underlying causes.
Murmurs are also graded on a scale from I to VI based on their intensity. A grade I murmur is very soft and may be difficult to detect, while higher-grade murmurs are louder and more easily heard. Although louder murmurs may raise concern for more significant disease, intensity alone does not determine severity. Some serious heart conditions may produce quieter murmurs, while some pets with louder murmurs may have minimal clinical impact.
Location and Patient History Also Matter
The location on the chest where a murmur is heard most clearly can provide additional diagnostic clues. Your veterinarian will also consider your pet’s age, breed, and overall health when determining what the murmur may indicate.
For example, myxomatous mitral valve disease is a common cause of a systolic murmur in older, small-breed dogs. In younger pets, a murmur may raise concern for a congenital heart defect, especially if it persists over time or is associated with other abnormal findings.
In cats, interpretation can be more complex. Some cats may have physiologic or stress-related murmurs that are not associated with structural heart disease. However, because murmurs in cats can also be linked to significant cardiac conditions, further evaluation is often recommended rather than relying on the sound alone.
Innocent vs. Pathologic Murmurs
Not every heart murmur is dangerous. Some young animals have innocent, also called physiologic, murmurs that are not caused by structural heart disease. Cornell’s veterinary cardiology guidance notes that many of these soft puppy murmurs are outgrown by about 6 months of age. These murmurs are typically quiet, found in otherwise healthy young pets, and may disappear as the body matures.
Pathologic murmurs are different. These are caused by an underlying condition affecting the heart or blood flow. In dogs, valve disease is a common reason, particularly in older small breeds. In cats, murmurs may be linked to cardiomyopathy or other cardiac changes, though they can also occur without significant structural disease. The distinction between innocent and pathologic cannot always be made by auscultation alone, which is why additional testing is sometimes recommended.
Congenital and Acquired Causes
Some murmurs are congenital, meaning they are associated with conditions present at birth. Others are acquired later in life. Congenital causes may include abnormalities in heart valves or blood vessels. Acquired causes can include degenerative valve disease, cardiomyopathy, or systemic illnesses that affect circulation.
Age often helps guide the conversation, but it does not provide the answer by itself. A murmur in a playful young pet may still need further workup, while an older pet with a new murmur and symptoms may need a more urgent cardiac evaluation.
What Testing May Be Recommended After a Murmur Is Found
The heart murmur itself is not treated directly. Instead, your veterinarian focuses on identifying the cause and deciding whether the heart is functioning normally. Depending on the exam findings, which may involve chest radiographs, blood pressure measurement, bloodwork, an electrocardiogram, or an echocardiogram. Of these, echocardiography is often the most useful test for understanding the structure and function of the heart.
An echocardiogram is an ultrasound of the heart. It allows a veterinarian, often a veterinary cardiologist, to see how the chambers and valves are working and whether blood flow is moving abnormally. The Merck Veterinary Manual notes that definitive diagnosis of many congenital cardiovascular anomalies typically requires echocardiography. This is one reason your veterinarian may recommend referral even if your pet seems comfortable at home.
- Chest x-rays can help assess heart size and look for signs of fluid in or around the lungs.
- Bloodwork may help identify conditions such as anemia or other systemic contributors.
- Blood pressure measurement can provide important information, especially in cats.
- An echocardiogram gives the clearest picture of heart structure and blood flow.
- Follow-up exams help monitor whether the murmur or symptoms are changing over time.
Are Some Breeds More Likely to Develop Heart Disease?
Breed can play a role in a pet’s risk for certain heart conditions, but it should always be considered as part of the bigger picture rather than used as a diagnosis on its own.
In dogs, older small-breed patients are more commonly affected by myxomatous mitral valve disease, which often results in a left-sided systolic murmur. Cavalier King Charles Spaniels are particularly known for having an increased risk, although many other small breeds may also develop this condition over time.
In cats, heart murmurs may be present with or without underlying heart disease, which can make interpretation more nuanced. Certain breeds, including Maine Coon cats and Ragdolls, are associated with inherited forms of hypertrophic cardiomyopathy in some lines. However, heart disease can still occur in mixed-breed cats and in breeds not typically considered high risk.
While breed information can help guide your veterinarian’s assessment, it is only one piece of the overall evaluation. Diagnostic testing is often needed to determine the underlying cause and significance of a heart murmur.
What Treatment Depends On
There is no single treatment for a heart murmur because the murmur is only a sign. Treatment depends on the cause, the severity of the disease, and whether the pet is showing symptoms. Some pets only need periodic monitoring. Others may need medication, lifestyle adjustments, dental or anesthesia planning, or referral to a cardiologist. In select congenital cases, interventional or surgical treatment may be considered.
The most important takeaway is that early detection can be valuable. A murmur heard during a routine exam may lead to testing that identifies heart disease before serious symptoms develop. That does not mean every murmur is an emergency, but it does mean the finding deserves thoughtful follow-up and a plan tailored to the individual pet.
When to Call Your Veterinarian About a Heart Murmur
If your pet has been diagnosed with a murmur, ask what signs should prompt a faster recheck. Coughing, increased breathing effort, tiring easily, weakness, collapse, fainting, a swollen abdomen, or a noticeable drop in activity level all warrant attention. Cats can be especially subtle, so decreased activity, hiding, or changes in breathing should not be ignored.
Routine wellness visits remain one of the best ways to monitor heart health over time. A murmur that was not present before, or one that changes in intensity, can help your veterinarian decide when further testing is needed. For many pets, careful monitoring and timely evaluation make a real difference.
If you have questions, we would love to answer them for you. Please give us a call at the office at (954) 722-2100, or you can email us at [email protected]. Our staff would love to talk with you!
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