What Causes Heart Murmurs

What causes heart murmurs?

Heart murmurs are common conditions that affect up to 1% of the population. They occur when there is a blockage or obstruction in one of the blood vessels supplying oxygenated blood to your heart. When this happens, it means that less blood reaches your heart, which can cause irregular heartbeat and even sudden death.

The most common type of heart murmurs is called atrial fibrillation. Atrial fibrillation occurs when the ventricles (the chambers where blood flows) in both sides of the heart become blocked or under-filled with fluid. These abnormal electrical signals cause the rhythm to change from regular to erratic, and then back again.

Atrial flutter is another type of heart murmurs. This condition affects the left side of the heart. A small amount of blood does not get into either ventricle and instead enters other parts of the body through veins and arteries. These blood vessels can lead to problems such as high pressure in the legs, chest pain, or difficulty breathing.

A third type of heart murmurs is known as ventricular tachycardia (VT). This condition is where the lower chambers of the heart (ventricles) become over-filled with blood. The muscles in these chambers flutter causing the chambers to contract more than they should. This condition can lead to other problems such as:


Heart attack

Sudden cardiac death

Other conditions that can cause heart murmurs are known as abnormal heart sounds. These are usually the cause of congenital heart defects. Other conditions can occur such as:

Blocked or narrowed blood vessels

Heart attacks

Atherosclerosis (plaques in the blood vessel walls)

Enlarged heart muscles due to a disease process (cardiomyopathy)

Defective aortic valve, causing aortic insufficiency

Most children with congenital heart disease develop some form of heart murmurs. The most common heart murmurs in these children are the following:

Isovalvar aortic stenosis

Mitral stenosis

Patent ductus arteriosus (abnormal opening between arteries)

Pulmonic stenosis

Tricuspid stenosis

A rare heart problem that causes heart murmurs is Ebstein’s anomaly. This is a congenital disorder where the tricuspid valve does not form properly. The tricuspid valve is responsible for regulating blood flow between the right atrium and right ventricle.

Most congenital heart defects cause murmurs shortly after birth, however, not all congenital heart diseases may cause a murmur, even if they are serious. It is important to get a proper diagnosis before birth by having a fetal echocardiogram. This test uses an ultrasound to take images of your baby’s heart. It can detect most congenital heart conditions.

In rare cases, heart murmurs can be a sign of a non-cardiac condition. For example, blood flow through the liver causes a whooshing sound known as a Hepatomegaly. In these cases, the condition is not dangerous and does not affect the heart or its functions.

Another non-cardiac cause of heart murmurs is the presence of an arteriovenous fistula which is an abnormal connection between an artery and a vein. This causes a whooshing sound known as a bruit.

Treating Heart Murmurs

In most cases, a routine visit to your pediatrician or family doctor will be sufficient to rule out any serious heart conditions. In some cases an electrocardiogram (ECG) might also be necessary. Usually if no other symptoms are present and the murmur doesn’t disrupt your daily life then there is no need for any treatment. In serious or specific cases, your doctor may recommend further testing.

This can include blood tests, chest x-rays or other imaging tests.

Most congenital heart murmurs are not a cause for concern and will disappear once the child grows out of them. Congenital heart murmur that are the result of a more serious condition can lead to further complications as the child grows older. In some cases, surgery may be necessary to repair the defect or defects. If you have any questions about your child’s murmur or its cause, contact your doctor.

Sources & references used in this article:

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Heart murmurs in horses: determining their significance with echocardiography by VB REEF – Equine Veterinary Journal, 1995 – Wiley Online Library

Heart murmurs in pediatric patients: When do you refer? by ME McConnell, SB Adkins III, DW Hannon – American family physician, 1999 – aafp.org

Deep neural networks for the recognition and classification of heart murmurs using neuromorphic auditory sensors by JP Dominguez-Morales… – IEEE transactions on …, 2017 – ieeexplore.ieee.org

Assessment of the prevalence of heart murmurs in overtly healthy cats by E Côté, AM Manning, D Emerson… – Journal of the …, 2004 – Am Vet Med Assoc

Evaluation and management of heart murmurs in children by JE Frank, KM Jacobe – American family physician, 2011 – aafp.org

Heart murmurs in newborn infants by RA Lyon, LW Rauh, JW Stirling – The Journal of Pediatrics, 1940 – Elsevier

Management of incidentally detected heart murmurs in dogs and cats by E Côté, NJ Edwards, SJ Ettinger, VL Fuentes… – Journal of Veterinary …, 2015 – Elsevier