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Understanding Heart Murmurs in Dogs
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Understanding Heart Murmurs in Dogs

Critter Culture Staff

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A heart murmur is an abnormal heart sound caused by atypical pumping of the heart. Doctors and veterinarians can identify heart murmurs with a stethoscope. Treatments and prognosis of murmurs in dogs depend on the underlying cause, as well as the dog's health, age, and breed. Caught early, heart murmurs often indicate a defect or disease that can be treated or managed. When your dog is diagnosed with a heart murmur, asking your veterinarian the right questions will ensure you know what to expect and how best to care for your dog.

1

What Is a Heart Murmur?

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The contraction and relaxation of the heart muscle delivers blood throughout the body by way of the blood vessels. A heart murmur occurs when the normal pumping of the heart is disturbed by an abnormal flow of blood. This disturbance may stem from a defect, disease, or infection of the valves or vessels of your dog's circulatory system, or the blood itself.

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2

How is a heart murmur diagnosed?

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The veterinarian can usually diagnose a heart murmur during your dog's annual exam. In more severe cases, your dog may begin to exhibit symptoms of a murmur that prompt you to make an appointment. These symptoms include trouble breathing, loss of appetite, weight loss, pale gums, and lethargy. If the vet discovers a murmur, he or she may perform some tests to determine the location of the murmur and any underlying diseases or conditions. Tests include echocardiograms, electrocardiograms, and blood tests.

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3

How is a heart murmur treated?

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Treatment depends on the underlying cause of your dog's murmur. The vet may prescribe medication for treatable conditions such as hypothyroidism, heartworm, and anemia. Surgery can correct certain structural heart defects. Often, innocent murmurs that do not cause harm to your dog require no treatment at all and may resolve on their own, though they should be regularly monitored.

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4

What causes heart murmurs in dogs?

heart murmur cause disease defect HAYKIRDI / Getty Images

Abnormalities in blood flow result from structural or functional abnormalities of the dog's heart, vessels, or blood. Structural defects include improperly functioning valves, diseased valves or vessels, and obstructions. Diseases and infections affecting the blood are functional irregularities. Causes often depend on the type or murmur, which may be classified as systolic, diastolic, or continuous.

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5

Systolic heart murmur

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In systole, the heart contracts and pumps blood through the arteries that supply the body with oxygenated blood. This is the first heart sound in a normal heart beat. A systolic heart murmur, then, occurs when the heart contracts and pumps blood, and it is the most common type of murmur in dogs. Systolic heart murmurs most often result from a narrowing of the heart's left ventricle or pulmonary artery in subaortic or pulmonary stenosis, respectively. Other causes include some types of heart failure, endocarditis, anemia, hypothyroidism, and heartworm.

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6

Diastolic Heart Murmur

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Diastole refers to the relaxation of the heart, when the veins empty deoxygenated blood into the organ. A diastolic heart murmur occurs when the heart relaxes. Aortic insufficiency is the most common cause of a diastolic murmur in dogs and occurs due to an improperly functioning aortic valve, which results in the heart leaking blood. Narrowing of the mitral and triscupid valves might also cause a diastolic murmur.

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7

Continuous heart murmur

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A continuous heart murmur occurs in both systole and diastole, occurring throughout the normal contraction and relaxation cycle of your dog's heart movements. The most common cause is patent ductus ateriosus, a congential defect. Aortic regurgitation and aortic stenosis with aortic regurgitation might also lead to a continuous heart murmur.

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8

Do all murmurs sound the same?

veterinarian listening to a dog's heartbeat using stethoscope FatCamera / Getty Images

Heart sounds in a murmur or heart murmur qualities vary depending on underlying factors. Your veterinarian will listen for the particular quality in your dog's murmur to make a judgement on the type and cause. There are four common qualities:

  • Plateau murmurs are uniformly loud
  • Crescendo-decrescendo murmurs rise and then fall in volume
  • Decrescendo murmurs begin loud and then decrease in volume
  • Continuous murmurs are machine-like in volume and pattern

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9

What are heart murmur grades?

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Your veterinarian will grade your dog's heart murmur according to its severity, on a scale from I to VI. Grades I and II can be heard only through a stethoscope and are typically the least concerning. Most serious heart murmurs are graded III or higher. Grade IV murmurs are audible on either side of the chest. The most concerning and potentially threatening murmurs, grades V and VI are the loudest murmurs and can be felt through your dog's chest without instruments.

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10

What happens next?

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Your dog's prognosis depends on the underlying cause and her overall health, age, and breed. Due to the variability of a heart murmur's outcome, only your dog's veterinarian can provide an accurate prognosis. Murmurs can often be managed or, in some cases, reversed entirely through medication or surgery. A severe murmur might indicate a defect, infection, or disease that has progressed toward heart failure. Depending on the stage of heart failure, the likelihood of survival may be low. In such cases, treatment may be confined to relieving symptoms and ensuring your dog is as comfortable as possible.

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11

Diagnostic tests to understand your dog's heart murmur

dog getting an ekg

When your vet suspects a heart murmur, they'll likely recommend a series of tests to get to the heart of the matter. An electrocardiogram (EKG) is the first step, tracing the heart's electric dance to spot any irregular rhythms. Blood pressure measurements are like checking the plumbing, ensuring the circulatory system's pressure isn't putting a strain on the heart. Ultrasounds and chest X-rays act as windows to the soul, or in this case, the heart, revealing its inner workings and structure. And for the pièce de résistance, the Cardiopet ProBNP test, which sniffs out heart stress like a detective, alerting to damage long before other symptoms may appear. These tests aren't just diagnostics; they're a roadmap to your dog's heart health.

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12

Mitral valve disease: A common heartbreaker

dog at vet

Mitral valve disease might sound like a complex tango of medical jargon, but it's a common dance partner for heart murmurs, especially in the ballroom of older and smaller dog breeds. It starts with a faulty valve, a small defect that lets blood waltz the wrong way in the heart's chambers, creating that telltale murmur. In the early stages, your dog might not miss a beat, but as the condition progresses, it can lead to a more serious condition, congestive heart failure. Early detection and a treatment plan can keep the music playing for your furry friend, ensuring many more happy dances together.

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13

Lifestyle changes for a happier, healthier heart

Weimaraner Dog running in the countryside Brighton Dog Photography / Getty Images

Think of your dog's heart as a drum, setting the rhythm for their life. When a murmur throws the beat off, sometimes it's the daily routines that can bring the tempo back. A diet that's easy on the heart, with less salt and tailored nutrients, can keep the blood flowing smoothly. And just like a good drum needs a regular, gentle touch, a dog with a heart condition benefits from exercise that's just right—not too hard, not too soft. It's all about finding that perfect rhythm that keeps tails wagging and hearts beating at their best.

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14

The genetics of heart murmurs in dogs

Two purebred Cavalier King Charles Spaniel dogs without leash outdoors in the nature on a sunny day. Bigandt_Photography/ Getty Images

In the diverse canine family, some breeds march to the beat of a different drum, especially when it comes to heart health. Breeds like the Cavalier King Charles Spaniel often carry a genetic tune that predisposes them to heart murmurs. Knowing this, breeders and pet parents can be on the lookout for early signs of heart murmurs and take steps to address them sooner. It's a bit like knowing the family history at a reunion—you know what to watch for and how to keep everyone dancing to the beat of a healthy drum.

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15

When to consult a veterinary cardiologist

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Sometimes, a general vet's stethoscope isn't enough to decipher the complex rhythms of a dog's heart murmur. That's when the maestro of heart health, the veterinary cardiologist, steps onto the stage. These specialists have the expertise to conduct in-depth examinations and prescribe treatments that can turn a worrisome murmur into a manageable condition. Whether it's considering surgery for a tricky heart valve or fine-tuning medications, a cardiologist can help compose a care plan that's music to a pet owner's ears—and a balm for a dog's heart.

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