Heart Murmurs in Cats: Should You Be Worried?

Heart murmurs in cats, also known as cardiac murmurs, can be a sign of heart disease. This is not something that you should ignore and hope it will go away on its own. Unfortunately, some breeds of cats are more prone to developing heart problems than others. The good news is that if your cat has been diagnosed with a heart murmur by your veterinarian, there are several treatments available depending on the type and severity of the problem. Read on to find out more.

What are heart murmurs in cats?

A heart murmur is an abnormal sound that can be heard when listening to your cat’s heartbeat. It is caused by turbulent blood flow through the heart and may indicate a problem with the structure or function of the heart.

There are many different types of heart murmurs and they can vary in intensity from hardly noticeable to very loud. Some heart murmurs may cause no symptoms at all, while others may be associated with shortness of breath, exercise intolerance, or even congestive heart failure.

Structure of the heart:

The heart is a four-chambered organ that pumps blood throughout the body. The two upper chambers (atria) receive blood from the body and the two lower chambers (ventricles) pump blood out to the body. The septum separates the atria from the ventricles and has an opening in it called the foramen ovale which allows blood to flow between the atria and ventricles before birth. The valves in the heart open and close to regulate blood flow through the heart.

The most common cause of a heart murmur in cats is an abnormal opening or narrowing of one or more of the valves in the heart.

Cat on cushion

Heart murmur in cats symptoms?

There can be many different symptoms associated with heart murmurs in cats, depending on the severity and type of murmur. Some cats may show no signs at all, while others may have more serious symptoms such as:

  • Weakness and shortness of breath
  • Difficulty breathing: Breathing more rapidly than usual and reduced exercise
  • Coughing
  • Weight loss
  • Fainting or syncope (temporary loss of consciousness)
  • Stunted growth in kittens
  • Sudden paralysis of the back legs
  • Sudden death: the most common cause of sudden death in cats is heart disease

Congestive heart failure

This is the most common symptom of heart disease in cats. When the heart isn’t working properly, it can’t pump all of the blood out to the body. The extra blood backs up and causes fluid to build up in the lungs (pulmonary edema), liver (hepatomegaly), and abdomen (ascites). Cats with congestive heart failure may be weak, have a poor appetite, lose weight, and become short of breath.

Blood clots

Blood clots can form in cats with heart disease as a result of irregular blood flow. These clots can break loose and travel to other parts of the body, like the brain or lungs. If they get lodged in an artery supplying blood to the legs, the leg may become paralyzed.

Causes of heart murmur in cats

There are many different causes of heart murmurs, which can be classified as either congenital heart disease (something the cat is born with) and Acquired heart disease (something the cat develops as it gets older).

Physiologic or Flow Murmur (innocent heart murmur): This is a non-threatening cause of a heart murmur in healthy adult cats. They do typically still require a veterinary evaluation to make sure there is nothing else going on, but usually, no treatment is necessary.

Innocent Kitten Murmur (innocent murmur):

This is a harmless cause of a heart murmur in young kittens. It happens in kittens up to about five to six months of age. It’s caused by the kitten’s fast heart rate and blood flow through the heart valves is turbulent. If the murmur persists after the kitten is 6 months old, it is usually time for a full examination.

Structural Cardiac Disease:

This is the most serious type of heart murmur, as it indicates there is a problem with the heart’s structure. Structural heart disease can be congenital (present at birth) or acquired (develops as the cat gets older).

Congenital Heart Defects:

  • Ventricular Septal Defect: A kitten can be born with a hole in the ventricular septum, which is a part of its heart that separates the left and right chambers. It keeps blood from flowing into the wrong chamber. If there is a small hole, there may not be any signs at all. But when it gets larger, signs will start to show up. Signs are typically seen when the cat has a medium or large hole in its heart. This can lead to congestive heart failure if it becomes very large. (tufts reference https://heartsmart.vet.tufts.edu/heart-diseases-cats/)
  • Patent Ductus Arteriosus is the second most common heart defect in cats. When a cat is developing, it has a blood vessel that connects the Aorta (leading away from the heart) and pulmonary artery (leading to the lungs). After birth, this blood vessel should close up. But when it does not, there will be too much blood flowing from the heart to the lungs. Heart failure can happen in kittens with PDA but if they are treated by a veterinarian early enough, surgery can fix it.
  • Mitral valve dysplasia: A less common heart defect in cats is mitral valve dilatation. The blood flow from the left atrium to the left ventricle is controlled by the mitral valve. When a cat has MVD, the blood does not flow properly and builds up in the left atrium. Cats with MVD may be weak and exhausted. Blood clots may develop as a result of MVD and can result in sudden paralysis if they get lodged in the blood supplying the spinal cord.

Acquired Heart Disease

Most forms of heart disease in cats are acquired in adulthood such as myocardial disease. Some develop due to genetic predisposition while others may be connected to other health issues.

Myocardial disease: This is a weakness or thickening of the heart muscle. The most common heart disease in adult cats is called Hypertrophic Cardiomyopathy (HCM). This is a disease of the heart muscle. When the heart muscle becomes weak, it can’t pump blood efficiently and this leads to a build-up of fluid in the lungs (pulmonary edema) and other tissues. It can lead to symptoms, like congestive heart failure (see below), blood clots, and lethargy. Predisposed cat breeds include the Maine Coon, British Shorthair, Persian, Ragdoll, and Sphynx

Systemic Disease: Some other diseases can cause secondary heart murmurs. This includes infections, high blood pressure – especially from kidney disease, hyperthyroidism (high thyroid hormone levels – similar to goiter in humans)which is common in older cats, and anemia.

I highly recommend this video for a simple explanation of heart murmurs

Risk factors

There are a few other risk factors that can increase the chances of your cat developing heart disease, including:


The older a cat gets, the more likely it is to develop heart disease.


Male cats are more prone to heart disease than female cats.


Overweight and obese cats are at an increased risk of developing heart disease as well as many other diseases. Extra fat around the heart, as well as inflammatory mediators produced by fat tissue, can have detrimental effects on healthy normal hearts.


There are some breeds of cat that are more susceptible to heart murmurs including:

  • Maine Coon: This is a breed of cat that is predisposed to hypertrophic cardiomyopathy
  • Siamese: This is a breed of cat that is predisposed to a heart condition called mitral valve prolapse
  • Persian
  • Oriental Breeds
  • Norwegian Forest Cat
  • Ragdoll
  • Sphynx
  • British and American Shorthair

How are heart murmurs diagnosed?

A heart murmur is not a diagnosis, but it is a sign that something may be wrong with your cat’s heart. The most common way to diagnose a heart murmur is with a physical examination. Your veterinarian will listen to your cat’s heart and may be able to hear the murmur just by listening with a stethoscope.

The intensity of the heart murmurs will also be graded while the stethoscope is placed on the cat’s chest. This grading is done on a scale of I to VI, with I being barely perceptible and heard only on one side of the chest. Grade I is barely audible, and it may be felt only on one side of the chest. The loudness intensifies by Grades III and IV. It may be heard in more than one area, and its vibrations can easily be felt through the cat’s chest wall.

If your cat has other symptoms, like weight loss or breathing problems, your veterinarian may also order some other diagnostic tests such as blood tests, chest x-rays, and a cardiac ultrasound of the heart and chest. Your veterinarian may also refer you to a veterinary cardiologist. Veterinary Cardiologists are specialist veterinarians that have undergone several extra years of training.

Cat heart murmur treatment

The treatment for a cat with a heart murmur will depend on the cause of the murmur. If it’s caused by an infection, your veterinarian may prescribe antibiotics. If it’s due to congestive heart failure or acquired heart disease, your veterinarian may prescribe medications to help the heart pump more efficiently, like diuretics (water pills) and ACE inhibitors. Please keep in mind that medications prescribed will not fix the heart but rather make your cat feel more comfortable by helping the heart function more efficiently. If it’s due to a structural problem with the heart, your veterinarian may refer you to a veterinary cardiologist for surgery.

Thanks for reading! Anytime you think something might be wrong with your cat, it’s important to take them to the veterinarian. Early detection and treatment of heart disease can prolong your cat’s life.

Summing Up

Heart murmurs are one of the most common types of heart disease in cats. Although they can occur in any age group, they are most commonly seen in kittens and young cats. Heart murmurs are caused by a change in the structure of the heart, which can interfere with the normal flow of blood. Symptoms of a heart murmur may include lethargy, exercise intolerance, and sudden death. Treatment for a heart murmur typically involves medication to improve blood flow and reduce congestion. In some cases, surgery may also be necessary. With early diagnosis and proper treatment, many cats with heart murmurs can live long and healthy lives.

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