Heart Murmurs in Cats: Symptoms, Causes, Diagnosis, and Treatment

Updated on July 23, 2019
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Trained in dentistry, Sree is currently studying lab sciences. She enjoys researching various health topics and writing about her findings.

There are a lot of common conditions in cats that people tend to overlook which may indicate a more serious problem. Heart murmurs, although common especially in kittens, are sometimes linked to the possibility of a heart abnormality. In some cats, heart murmurs appear and eventually disappear. For other cats, a murmur may indicate an underlying and possibly severe heart condition.

What Are Heart Murmurs?

Heart murmurs are extra sounds in addition to the "lub-dub" rhythm of the heart. They are made by unusually turbulent blood flow in the cat's heart. These extra sounds are only audible when listening to a cat's heart with a stethoscope. Heart murmurs are not a disease but are considered an abnormal finding.


How Heart Murmur Sounds Occur

There are four chambers in a cat's heart: the tricuspid valve, the pulmonic valve, the mitral valve, and the aortic valve. Blood flows through the tricuspid valve first, and then the pulmonic valve before obtaining oxygen from the lungs. Oxygenated blood flows back to the heart through the mitral valve and finally the aortic valve for body distribution. Heart murmurs are turbulent-like sounds that are created by disturbed blood flow in the heart valves, ventricles, or atria. They may be caused by increased blood flow, dilated pathways, or the clotting of blood.

Causes of Heart Murmurs

Heart murmurs are caused by changes in the heart's normal blood flow. They can occur when blood leaks through the heart valves, or when there are heart muscle defects like contractions or dilation. When either the blood vessels or heart chambers narrow, heart murmurs will occur as well. Common causes of heart murmurs include:

  • Some cats are born with congenital, "innocent" heart murmurs. They don't seem to be associated with any disease, and they gradually disappear as the kitten grows older.
  • Heart murmurs in adult cats that are not linked to a diagnosable disease are called "physiological" murmurs. They are often caused by stress and gradually disappear when the cat's environment is changed.
  • Heart murmurs can develop over a cat's lifetime but remain benign.
  • Heart murmurs may indicate an underlying heart disease. It may indicate a blockage or clogging of the arteries, causing a disturbance in the heart's blood flow.
  • Other conditions such as anemia can also cause heart murmurs, accompanied by other symptoms like lethargy and anorexia.
  • Cardiomyopathy (a disease of the heart muscle) can cause heart murmurs.
  • Although heartworm is rare in cats, it can cause heart murmurs.
  • Systemic illnesses such as thyroid disease or high blood pressure may also cause heart murmurs.


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Other Symptoms to Watch Out for

Heart murmurs are only one symptom, and when accompanied by other symptoms, should there be a significant underlying problem. Here are the following accompanying symptoms to watch out for:

  • Rapid breathing or difficulty in breathing
  • Lethargy or consistent weakness
  • Loss of appetite and/or unexplained weight loss
  • Collapsing
  • Noisy breathing or a congestion
  • An extra "gallop" sound in the heartbeat

Should any of the symptoms above show, the cat should be taken to the veterinarian for proper diagnosis. Certain tests may be required to properly assess the problem.

The Risks of Undiagnosed Heart Murmurs

While heart murmurs are more of a symptom than a disease, not having the cat diagnosed can pose serious health risks. Depending on the type and stage of the heart disease, the risk and required medical attention will vary. A cat with a heart murmur may grow weak and lose its appetite if an underlying illness is untreated, leading to other forms of sickness that cause further problems. In some cases, sudden death can occur too.

Interesting Fact

Heart murmurs don't exactly sound like "murmurs." In fact, they may seem more like "whooshing" sounds or additional extraordinary beats as opposed to the normal "lub-dub" heart sound.

The Diagnosis of Heart Murmurs in Cats

There is a grading system to indicate the severity of a cat's heart murmurs. The system is mostly based on how loud the heart murmurs are and which part or valve area it is coming from. According to the criteria, heart murmurs may be graded from I to VI, with Grade I as the mildest while Grade VI the most severe. In any case, the loudness of the murmur does not indicate the severity of the illness.

There are some cases where heart murmurs are not connected at all with any cat illness and even the loud sounds indicate a relatively mild form of the disease. Should the veterinarian suspect or discover clinical signs of a disease, the following procedures/examination will be given:

  • Chest Radiograph: An x-ray of the heart will show if there is any physical abnormalities in the cat's heart. Some diseases cause certain parts, such as the atrium, to grow progressively thicker and appear quite enlarged in an x-ray.
  • Echocardiography: A cardiac ultrasound scan is a painless and faster form of procedure which produces a more detailed image of the heart. This will show images of the valve and helps the veterinarian determine if there is any clogging, enlarged arteries or other abnormalities.

In some cases, an ECG or electrocardiogram may be required, depending on the veterinarian's assessment or findings. Blood work, a urinalysis, and blood pressure measurement may also be performed. The cat may undergo repeat examinations if the heart murmurs persist or other symptoms appear.

Depending on the assessment and findings, the veterinarian will provide a treatment plan for the cat's heart murmurs. Most conditions which cause murmurs are treatable with medicine. Surgery is rarely needed and is not recommended in most cases. The prognosis will still depend on the type of disease found in the cat and its severity. Early detection and immediate treatment will provide a higher chance of recovery and healing.


Hypertrophic Cardiomyopathy (HCM)

This disease is not the most common cause of heart murmurs but is the most common type of heart disease found in cats.

  • Characteristics: Hypertrophic cardiomyopathy affects young and adult cats. It may affect elderly cats but is not as commonly found in them. A cat with HCM suffers from a thickened left ventricle. If left untreated, the left ventricle of the heart can cause clogging and enlargement of the left atrium. Most cats with HCM show little signs of it or develop symptoms that suggest problems, and often live normal lives. Some cats do show and develop symptoms but only during the advanced stage of the disease.
  • Severe Cases: Advanced or severe cases of HCM causes paralysis in the hind legs of the cat. This happens because the enlarged atrium has already caused a formation of blood clot in the heart. This clot usually dislodges and gets stuck in the narrow end of the aorta—the largest artery of the cat's body which is responsible for distributing the blood supply to the hind legs.
  • Risks: In severe cases of HCM, the cat will show signs of pain before experiencing temporary paralysis. In some cases, the onset of paralysis is sudden, making most owners think their cat had a road accident or had been abused. Death can also occur suddenly. In some cases, treated cats with severe HCM may need maintenance drugs to prevent a possible recurrence of blood clotting.
  • Symptoms: Heart murmurs are the most common symptom of HCM, accompanied by a loss of appetite, difficulty breathing, and pale gums. The cat may often be lethargic.
  • Treatment: Certain heart drugs may be prescribed as treatment. In some cases, a diuretic injection or tablets may be given to clear the fluid in the heart.

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This article is accurate and true to the best of the author’s knowledge. It is not meant to substitute for diagnosis, prognosis, treatment, prescription, or formal and individualized advice from a veterinary medical professional. Animals exhibiting signs and symptoms of distress should be seen by a veterinarian immediately.


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