What Causes a Newborn Heart Murmur?

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  • Written By: N. Madison
  • Edited By: Jenn Walker
  • Last Modified Date: 25 March 2020
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There are a few basic contributing factors that may cause a newborn heart murmur. The most common include small blood vessels, faster blood flow through the aortic and pulmonary valves, and naturally thinner chest walls that make blood flow sounds more apparent. Sometimes, however, a birth defect of some type causes a newborn heart murmur. For example, a newborn may have a hole in the heart or a heart valve abnormality that causes a heart murmur. Most newborn heart murmurs are innocent, however, which means they do not cause health problems or require medical treatment.

Heart murmurs are basically abnormal sounds that occur when a person’s heart beats. For example, a newborn heart murmur may cause a sound like a whoosh or a swish that can be heard via a stethoscope. In most cases, the causes of a heart murmur in a newborn baby are innocent and not cause for alarm. The presence of a heart murmur usually does not indicate a need for treatment. In some cases, however, potentially serious birth defects are at the root of newborn heart murmurs.


The causes of an innocent newborn heart murmur often include such factors as smaller blood vessels that lead to the lungs and produce sounds as the blood flows thorough. This is usually normal, and blood flow eventually helps blood vessels to grow in size. Sometimes blood flow across the aortic and pulmonary heart valves creates abnormal sounds due to the fact that blood travels at a higher speed in children. Additionally, the fact that newborns' chest walls are typically thinner than adults' may make such sounds more obvious.

Unfortunately, a newborn heart murmur may also appear as the result of something more serious. For example, it is sometimes the result of a hole that develops in the walls of a baby’s heart prior to birth. The seriousness of this type of birth defect depends on where in the heart the holes are located and the size of them.

In some cases, a newborn heart murmur is also caused by abnormalities in his heart valves. For example, this may occur when a newborn’s heart valves are too tight and don’t allow for adequate blood flow. Likewise, doctors may hear a heart murmur when a newborn’s heart valves fail to close as they should and allow the leaking of blood.



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