Pet InfoRx®
Heart Murmurs in Cats

Your cat seems perfectly fine or has just lost a little weight, but your veterinarian has just informed you that your cat has a heart murmur.

This information prescription will explain what some general causes of heart murmurs are and what things you need to pay attention to when you have a cat with a murmur.


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HCM and Heart Murmurs

cat heart murmur detected with stethoscope

The most common heart disease that causes heart murmurs in cats is Hypertrophic cardiomyopathy (HCM). The walls of the heart thicken, and over time the heart becomes stiffened and cannot function properly. As time progresses, blood flow from the heart becomes blocked. HCM appears to be inherited in most cases, so genetics are believed to be a leading cause. Cats with untreated hyperthyroidism can also develop HCM.

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What Is A Heart Murmur?

Heart murmur is a term used to describe sounds, such as whooshing or swishing, that are heard when a veterinarian listens to the heart with a stethoscope. It is a vibration that is caused by turbulent and high-velocity blood in or near the heart. 

Heart murmurs are graded based on their intensity or loudness. Typically, a scale of I (one) to XI (6) is used. A Grade I murmur is barely able to be heard and may be inconsistent, whereas a Grade XI is the loudest and can felt by touching one’s hand to the heart region of the chest (this is called a thrill). The grading scale allows veterinarians to characterize the murmur and evaluate changes in conditions. The severity of the heart issue does not necessarily coincide with the grade. 

Benign or Physiologic Heart Murmur

If your cat is diagnosed with this type of murmur, then there's no impact on your cat’s life, and it's not harmful. The blood is circulating normally within the chambers of the heart and through the vessels. This is often the case when a murmur is detected in kittens between 6 to 8 weeks of age. Typically, the kitten will outgrow it by 4 to 5 months of age. Additionally, adult cats can have an intermittent murmur when they are stressed.

Pathologic Heart Murmur

This type is caused by disease. It is due to a structural problem within the heart. The most common type of pathologic murmur is caused by hypertrophic cardiomyopathy (HCM).

Functional or Extra-Cardiac Heart Murmurs

These are murmurs caused by issues outside the heart. They can result in temporary murmurs or if left untreated, permanent murmurs. Some issues that can cause these types of murmurs are:

  • Low levels of red blood cells (anemia)
  • Low levels of protein in the blood (hypoproteinemia)
  • Fever
  • Infection
  • High blood pressure
  • Hyperthyroidism: This is the most common cause of extra-cardiac murmurs. It can cause hypertrophic cardiomyopathy.
  • Severe dehydration
  • Conditions such as pregnancy, obesity, or malnutrition

NOTE: Kittens that are overloaded with intestinal parasites (worms) or fleas/ticks will suffer from anemia and hypoproteinemia, which can result in a murmur. Once those issues are treated and the anemia and hypoproteinemia are corrected the murmur can sometimes disappear.

Obvious signs are not always evident in all cats with heart conditions, but some you may notice are:

  • Weight loss
  • Difficulty breathing
  • Weakness

How Did This Happen?

Just because a murmur is detected, does not mean there is reason for concern

A heart murmur is the vibrational sound heard as blood moves within and near the heart. The cause can be harmless, due to abnormal changes in the heart itself, or due to disease or illness (see section above for a list).

To determine the exact reason why your cat has a heart murmur, your cat’s veterinarian will need to do a complete physical exam as well as run several diagnostic tests. These tests can include one or more of the following:

  • Blood work – Complete Blood Count (CBC), Chemistry Panel, Thyroid Panel
  • Chest radiographs – this can assess the size of the heart as well evaluate the blood vessels and lungs
  • Electrocardiogram
  • Blood pressure check

What You Should Do If Your Cat Has A Heart Murmur

Once your cat has been diagnosed with a heart murmur, you should have them evaluated by their veterinarian at least every 4 to 6 months. The sooner any changes in the grade of the murmur or other underlying diseases are detected, the sooner appropriate treatment can be started.

Your cat’s veterinarian may also recommend a referral for a veterinary cardiologist, depending on the cause behind the heart murmur.

You should watch for any of the following symptoms if you have been told your cat has a heart murmur or that they may have a heart condition. If noted, contact your veterinarian.

  • Weight loss
  • Decreased appetite
  • Weakness
  • Tiredness
  • Difficulty breathing or breathing abnormally
  • Congestion
  • Collapse

NOTE: Seek veterinary care IMMEDIATELY if you notice your cat open-mouth breathing, abnormal color to their gums and/or tongue (blue or gray), or if they collapse.

cat sleeping with heart murmur

Benign or Physiologic Heart Murmurs

These most often do not require any treatment except having your cat regularly examined by their veterinarian and monitored for any changes in health.

Pathologic and Extra-cardiac Heart Murmurs

These often require a combination of treatments that may include medications, special diets, and supplemental care. It is critical that you follow your veterinarian’s instructions carefully and give medications as directed. Additionally, regular diagnostic monitoring tests, such as blood work, blood pressure checks, etc., will be essential. If you notice anything abnormal about your cat, call a veterinarian immediately.

How Do You Know Things Are Improving?

Improvement will be based on the cause of the murmur.

If your kitten is diagnosed with a murmur between 6 to 8 weeks of age, it should resolve by the time they are 4 to 5 months old.

With pathologic murmurs, the severity of the disease state of the heart determines your cat’s improvement. For mild cases, improvement can be seen within a couple of weeks, and the average survival time is 3 to 5 years. Cats with this type of murmur with congestive heart failure will improve in a few weeks, but the average survival time is 3 to 18 months.

For extra-cardiac heart murmurs, improvement is based on the cause. If the underlying cause can be treated, anemia, for example, often the murmur will improve. But there may be other extra-cardiac causes that can be treated, but there has been damage to the heart. In this situation, improvements may take longer. For example, in advanced cases of hyperthyroidism, significant damage has occurred to the heart. While treatment for hyperthyroidism may help improve your cat’s general health, the damage to the heart will prevent the murmur from disappearing. Typically, with most underlying causes, your cat’s overall health will improve within 2 to 4 weeks.

How Do You Know When Things Are Not Improving? What You Should Do.

If your cat continues to lose weight, develops new symptoms, or the current ones worsen, contact your veterinarian immediately.

If your cat was started on any medications and you don’t notice any changes within a few days, contact your veterinarian.

NOTE: If your cat suddenly seems paralyzed in their hind legs and their paws are cold to the touch, seek veterinary care IMMEDIATELY. Your cat likely has a blood clot and needs immediate medical attention.

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How to Prevent This from Happening in the Future

For the most part, prevention isn’t possible, but early detection and treatment are. Having your cat regularly seen by their veterinarian for wellness exams is the best way to help your cat.


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