Heart murmur

The familiar “lub-dub” sound of the heartbeat is made by the rhythmic closing of the heart valves as blood is pumped in and out of the chambers. A heart murmur is an extra sound caused by blood flow within the heart. Instead of just “lub-dub”, the heartbeat may have an added hum, whoosh or rasp.

The sound comes from the vibration of blood as it moves through the heart, which is normally too quiet to hear through a stethoscope. Blood can flow in a way that creates a murmur for many reasons, including faulty valves, congenital heart disorders and anaemia.

A noisy heart is not always a sign of disease. Many children have “innocent” murmurs that need no treatment or observation. However, an innocent murmur and a harmful one can sound the same through a stethoscope, so medical tests are often needed to tell them apart.

How the heart works#

The heart is a double pump made up of four chambers, each sealed by valves that allow blood to flow in only one direction. The right upper chamber (right atrium) takes in deoxygenated blood from the body and pushes it into the right lower chamber (right ventricle). From there, an artery carries the blood to the lungs, where carbon dioxide is exchanged for oxygen.

Oxygenated blood enters the left upper chamber (left atrium). It is then pumped into the left lower chamber (left ventricle) and out into the body’s main artery (the aorta) to begin its journey around the body again.

Innocent murmurs#

A heart murmur is usually innocent and does not mean there is anything wrong. The murmur may simply be heard because the vibration of blood travelling through the heart is greater than usual, or because the heart sits close to the front of the chest and the stethoscope.

It is thought that around half of all babies and young children have innocent murmurs. They are called “innocent” because they are not linked to any disease or structural problem, and in most cases the murmur settles by adolescence. Because a stethoscope cannot always tell an innocent murmur from a harmful one, further tests are sometimes needed to rule out an underlying problem.

Symptoms#

Heart murmurs themselves often cause no symptoms and are frequently picked up only during a routine examination. Abnormal murmurs may be linked to heart disease, particularly conditions affecting the heart valves. Possible signs of underlying heart disease include:

• a blue tinge to the skin (cyanosis), caused by a lack of oxygen
• chest pain
• a fast heart rate (tachycardia)
• heart palpitations
• breathlessness
• fatigue

Causes of an abnormal murmur#

A murmur can be caused by faulty blood flow within the heart. Conditions that can lead to this include:

• Congenital heart disorders. During development before birth, the heart and blood vessels may not form properly. Blood flow may be blocked, blood may travel abnormally through the valves, or the heart itself may be underdeveloped.
• Mitral regurgitation. The mitral valve separates the left atrium from the left ventricle. When it does not close properly, blood leaks back into the atrium. Causes include rheumatic heart disease, infection of the valve (endocarditis), high blood pressure and congenital heart defects.
• Aortic regurgitation. The aortic valve separates the aorta from the left ventricle. When it does not close properly, blood leaks back into the ventricle. Causes include congenital heart defects, rheumatic heart disease, infection of the valve (endocarditis), Marfan’s syndrome and high blood pressure.
• Mitral stenosis. The opening of the mitral valve is abnormally narrow, restricting blood flow into the left ventricle.
• Aortic stenosis. The opening of the aortic valve is abnormally narrow, restricting blood flow into the aorta.
• Damage to the heart muscle. This can follow a heart attack or a heart infection, or arise as a complication of coronary artery disease or high blood pressure.
• Anaemia. When the blood cannot carry enough oxygen to the cells, the heart pumps faster to meet the body’s demand. Anaemia is not a disease in itself but a sign of a problem elsewhere in the body.
• Hyperthyroidism (an overactive thyroid). Excess thyroid hormone affects the heart in a similar way to anaemia.
• Stress. Emotional stress can sometimes change the force of the heartbeat and increase blood flow, as happens with anaemia and hyperthyroidism.

Diagnosis#

Finding the cause of a heart murmur may involve a number of tests, including:

• a medical history
• a physical examination
• a chest x-ray
• an electrocardiogram (ECG)
• blood tests
• an echocardiogram (a type of ultrasound scan of the heart)

Treatment#

Treatment depends on the cause and may include:

• Innocent murmurs. No treatment is needed, as the heart’s structure and blood flow are normal, just noisy.
• Faulty or leaking valves and congenital defects. Heart surgery may be needed to repair them, sometimes requiring open-heart surgery.
• Endocarditis or other infections. Antibiotics, and surgery in some cases.
• Anaemia. Often treated with iron supplements and dietary changes. More serious cases may need treatments such as a blood transfusion or removal of the spleen (splenectomy).
• Hyperthyroidism. Medication or surgery to return thyroid hormone levels to normal.

Key points#

• A heart murmur is a sound caused by blood flow within the heart.
• Many children have innocent murmurs that need no treatment or observation.
• Heart murmurs themselves often cause no symptoms.
• They are commonly innocent and detected only during a routine examination.
• Signs of underlying heart disease can include cyanosis, a blue tinge to the skin caused by a lack of oxygen.

Where to get help#