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Heart Murmurs in Cats

cat heart murmur

Normal hearts beat with a quiet flow of blood. A heart murmur occurs when blood flowing through the heart causes a sound that can be heard through a stethoscope and sometimes even felt by touch. The best way to describe this is like a wide, slow-moving river and suddenly a large obstruction such as a boulder rolls or falls into the river, causing the water to become turbulent as it flows around the stone, creating noise and sound. A heart murmur in a cat should always be further evaluated to determine the cause. Learn more about causes and what to do if your cat’s pDVM (primary veterinarian) hears a heart murmur while listening to their heart and lungs during a physical exam.

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Heart murmurs can be pathologic meaning the murmur is due to heart lesions that develop from the progression of heart disease and age. Heart murmurs can also be functional or physiologic and occur in young, growing cats.

Diagnosing the Cause of a Cat’s Heart Murmur

A heart murmur is a clinical sign that can be present at birth (congenital) or may develop (acquired). Murmurs may be noticed during a routine physical exam in a cat that has no signs or symptoms of disease.

If your cat has a heart murmur, your vet will discuss additional testing based on your cat’s physical exam findings, health status, history of illness, age, and risk.

Veterinarians often begin with x-rays of your cat’s chest to evaluate their heart and lungs. Echocardiography (also known as ultrasound) is the imaging test of choice to determine what is causing the heart murmur. Lab tests, including a complete blood count, chemistry panel, urinalysis, etc. help to determine a baseline and if your cat has any underlying issues or disorders that may contribute or be causing the murmur. NT-pro-BNP testing is a cardiac biomarker that is often used to determine the severity of a patient’s heart disease. This test is recommended in cats that have a murmur but no symptoms of heart disease.

Sick cats that have a heart murmur often need further diagnostic tests to determine if the murmur is associated with the illness. Cats that have a heart murmur along with symptoms of possible heart disease such as difficulty breathing, weakness, and exercise intolerance need further evaluation of their heart. Tests may include blood work, x-rays, and echocardiogram.

Heart murmurs associated with congenital heart disease include:

  • PDA (patent ductus arteriosis)
  • Aortic stenosis
  • Septal defects
  • Atrioventricular valve dysplasia
  • Tetralogy of Fallot
  • Other less common lesions

Heart murmurs associated with acquired heart disease include:

  • Mitral or tricuspid degenerative valvular heart disease
  • Anemia
  • Fever
  • Endocarditis
  • Diastolic dysfunction syndromes

Describing Heart Murmurs

Veterinarians describe heart murmurs by listening to the heart and lungs of a cat using a stethoscope. The murmurs are defined using the following terms:

  • Grade from softest to strongest: Grade I-VI/VI (Grade 1-6/6)
  • Location where the murmur is heard the loudest on the chest (left-sided, right-sided, high, low, etc.) and if it can be heard in other areas of the chest or neck.
  • Murmurs are described by when they occur during the heart cycle (systole, diastole) or if they are continuously heard throughout the cycle.

Heart Murmurs in Middle-Aged to Older Cats

In cats, heart murmurs can be caused by excitement (physiologic) or an underlying heart problem (pathologic). To distinguish between the two, an echocardiogram will have to be performed. The most common heart disease in cats in which a heart murmur is a prominent symptom is hypertrophic cardiomyopathy, which can lead to congestive heart failure. Some cats don’t show any symptoms during the early part of the disease before they develop congestive heart failure. Some already have congestive heart failure soon after diagnosis. And there are cats with hypertrophic cardiomyopathy that never develop congestive heart failure or exhibit any clinical signs of heart disease.

Cats with HCM may form a blood clot which can block a blood vessel causing severe pain and distress. This can show up as a cat that suddenly cannot use their back legs, is crying or vocalizing in pain, and their back legs feel cool to the touch. This condition is often called a saddle thrombus. Treatment is difficult and often unsuccessful. Unfortunately, cats often end up being put to sleep (euthanized).

If your cat has been diagnosed with hypertrophic cardiomyopathy, regular visits to your vet are necessary so an echocardiogram can be performed to monitor the progress of the disease.

Any middle-aged or senior cat can develop hypertrophic cardiomyopathy but breeds that are more at risk include the Maine Coon, Norwegian Forest Cat, British Shorthair, American Shorthair, Ragdoll, Devon Rex, and Sphynx.

Other Risk Factors

Heart murmurs can happen secondary to non-cardiac problems such as fever, infection, anemia, hyperthyroidism, extreme thinness, obesity, and pregnancy.

It is important to understand that some heart diseases may not have a murmur, meaning the absence of a heart murmur does not mean that a patient does not have heart disease.

Can heart murmurs be treated?

Treating a heart murmur begins with determining the cause. There are different medications available, depending on the diagnosis. Not all murmurs need treatment. Your vet will use their assessment of the severity or intensity of the murmur along with x-rays evaluating the heart size to determine the seriousness and outcome of the heart disease and necessary or recommended treatment(s).

Read more:

Your Pet’s Heart: A Guide to Understanding Heart Health in Dogs and Cats

Pulmonary Hypertension in Dogs and Cats

Atrial Fibrillation in Dogs and Cats

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