What is a heart murmur?

A normal heartbeat makes two sounds – lubb-dubb – which are the sounds made when your heart valves close during each heartbeat. Any extra sounds – such as whooshing or swishing – are called heart murmurs.

Heart murmurs can be there at birth (congenital) or can develop later in life. Heart murmurs aren’t a disease. They might or might not be a sign of an underlying heart problem.

Usually, heart murmurs can be heard only through a stethoscope (a medical device doctors use to listen to sounds in the body).

Heart murmur types

There are two types of heart murmurs: innocent murmurs and abnormal murmurs.

An innocent murmur means the heart is normal. They happen when blood flows more quickly than normal through the heart.

Abnormal heart murmurs are more serious. They are usually caused by an underlying heart problem, which may need treatment.

What causes a heart murmur?

Innocent murmurs happen when your heart rate and blood flow increases, because of:

• exercise
• pregnancy
• fever
• anaemia– not enough red blood cells to carry oxygen around the body; caused by having low iron levels
• hyperthyroidism– too much thyroid hormone in your body
• periods of rapid growth, such as adolescence.

Abnormal murmurs are mostly caused by an underlying heart problem, such as:

• heart disease at birth (congenital birth defects) – such as a hole in the heart
• hypertrophic cardiomyopathy – an increase in heart size
• stenosis – where the heart valves are too narrow or stiff
• regurgitation – where the heart valves don’t close properly
• diseases affecting the heart muscle – such as endocarditis and rheumatic heart disease.

Heart murmur diagnosis

Doctors are likely to first pick up heart murmurs with a stethoscope. They may order further tests to check whether it’s an innocent or abnormal murmur. These tests can include:

• electrocardiogram (ECG) – a machine that records the heart’s electrical activity
• chest X-ray – to check if the heart is bigger than normal, damaged or abnormal due to birth defects
• echocardiogram (cardiac echo) – a heart ultrasound
• cardiac catheterisation – dye is injected into the heart to help your doctor better see the heart on X-ray.

Are heart murmurs dangerous?

Most heart murmurs are not dangerous and don’t need to be treated. But all need to be checked by a doctor.