Pediatricians may sometimes hear an extra sound between heartbeats as blood moves through babies’ hearts. This is what doctors refer to as a heart murmur. In most cases, it is not a cause for concern, but sometimes it may indicate an underlying heart problem.

The heart has four chambers and four valves, which ensure that the blood flows in a single direction and prevent it from flowing back. When the heart pumps blood, it creates a steady “lub-dub lub-dub” sound as the heart valves in the heart chambers and arteries close.

Sometimes, a pediatrician listening to a baby’s heartbeat may report hearing an extra or abnormal sound between heartbeats.

This article discusses heart murmurs in babies, including the causes, who they affect, and the signs and symptoms. It also looks at the diagnostic process and treatment options for babies with heart murmurs.

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A heart murmur is any whooshing, rasping, or humming between the two heartbeat sounds. It happens when there is a turbulent blood flow in the heart. A doctor will be able to hear this sound using a stethoscope.

Heart murmurs are relatively common in children. Up to 72% of children will have a heart murmur at some point in their life.

Learn more about the heart’s anatomy.

There are three types of heart murmurs:

  • a systolic murmur occurs when the heart contracts
  • a diastolic murmur occurs when the heart relaxes between beats
  • a continuous murmur occurs throughout the cardiac cycle

Based on loudness, doctors grade heart murmurs on a scale of 1 to 6. They use 1 to describe a very faint sound and 6 to refer to one that is very loud.

Innocent vs. abnormal heart murmur

Harmless heart murmurs, which are known as innocent heart murmurs, are common in babies, young people, and adults. They are usually louder when a person is excited or has a fever or a cold, as increased activity or temperature makes the heart pump more blood.

These heart murmurs occur in a structurally normal heart and do not require any activity restrictions or other precautions. Most innocent murmurs fade or eventually disappear as a child grows up.

Abnormal heart murmurs are rare, especially in babies, affecting less than 1% of the general population. A heart defect or problem is usually the case.

In newborns, heart murmurs may happen as they switch from using their mother’s oxygen through the placenta to breathing for themselves. Changes in blood circulation can occur at this time.

In children, doctors will hear innocent murmurs in the following circumstances:

  • increased turbulent flow, which occurs in high cardiac output states such as anemia
  • vessel narrowing, which can occur when vessels stretch during phases of rapid growth, such as during adolescence
  • lung expansion after birth

On the other hand, abnormal heart murmurs are typically due to structural abnormalities that are present from birth, known as congenital heart defects. These include:

  • holes in the heart wall, known as septal defects
  • abnormal connections between the two main arteries of the heart
  • valve abnormalities, such as the valves being too thick, narrow, or small
  • cardiomyopathy, which makes the heart muscles too thick or weak to pump blood normally
  • reversed blood flow because of a leaky valve

Learn more about congenital heart defects.

Risk factors

Other conditions that may cause or contribute to heart murmurs include:

A child may also develop a heart murmur following an infection or another health condition.

People who have difficulty controlling diabetes or phenylketonuria while pregnant and those who caught rubella during pregnancy are at risk of having a baby with a heart murmur.

Babies and children with innocent murmurs usually experience no symptoms, making abnormal heart sounds the only indication of the condition.

However, symptoms can sometimes occur. Parents or caregivers should look out for the following signs:

In some instances, other than an abnormal heart sound, a potentially life threatening heart defect is asymptomatic, meaning that it produces no symptoms.

A 2020 review found that some newborns with asymptomatic heart murmurs have congenital heart disease.

A doctor will perform a detailed clinical examination and a thorough evaluation to identify the cause of a heart murmur.

If a healthcare professional suspects that a child has a heart problem, they may refer the child to a pediatric cardiologist, a doctor specializing in heart problems in babies and children.

The pediatric cardiologist will ask about the child’s medical history and symptoms. They will then use a stethoscope to determine whether the murmur is abnormal.

Grading murmurs

For the intensity, doctors use a grading scale of 1–6. Specialists typically evaluate murmurs with a grade of 4 or higher until proven otherwise.

  • Grade 1: The sound is softer than the heart sounds.
  • Grade 2: The sound is as loud as the heart sounds.
  • Grade 3: The sound is louder than the heart sounds.
  • Grade 4: The sound is the same as grade 3 but with a palpable vibration.
  • Grade 5: The sound is very loud, and doctors can hear it with the stethoscope barely on the chest.
  • Grade 6: The sound is very loud, and doctors can hear it with the stethoscope off the surface of the chest.

Tests

The doctor may also choose to do some tests to help further diagnose the cause of the heart murmur:

  • Chest X-ray: This test can check the size and shape of the baby’s heart and assess the blood vessels that deliver blood to and from the lungs.
  • Electrocardiogram: This test measures the heart’s electrical activity. It can also detect damaged heart tissue.
  • Echocardiogram: This type of test uses sound waves to assess the structure and function of the heart, including the movement of heart muscles.

A child’s treatment will depend on their age, symptoms, and general health, as well as the severity of the condition.

Innocent murmurs do not require treatment and tend to resolve with time. Some persist through adulthood but show no other symptoms. Innocent murmurs do not require constant monitoring, and children can lead normal lives.

If a condition or an issue with the heart causes the murmur, the doctor may focus on treating the primary disease. The murmur may go away or lessen once the doctor successfully treats the condition causing the murmur.

A doctor may prescribe medications and perform regular checkups and testing to monitor whether the condition is due to a structural abnormality. Some congenital heart disorders resolve on their own over months or years.

The doctor may recommend different procedures or surgeries depending on the underlying disorder.

Heart murmurs are common in children. Most of them are not a cause for concern and do not show other symptoms. Heart murmurs that occur alongside other symptoms may indicate an underlying heart problem.

It is essential for babies with a heart murmur to get a further evaluation to make sure that it is not due to an underlying heart issue. Parents or caregivers who notice symptoms such as shortness of breath, difficulty feeding, or clammy skin should make an appointment with a pediatrician for an assessment.