Many normal conditions may cause the blood to flow with turbulence, causing a murmur to be heard. These conditions do not necessarily indicate something is abnormal, nor do they cause an ill effect on the child’s health.
Among the conditions that may cause a normal (or innocent) murmur are:
Physiologic Peripheral Pulmonary Stenosis (PPS)
This murmur is typically heard at 1 to 2 months of age. Babies with this type of murmur are typically born with relatively small blood vessels to the lungs. After the main trunk of the pulmonary artery leaves the heart, it branches to the right and the left lung. Because babies are relatively thin from front to back, these branches come off at a sharp angle from the main lung artery. As blood goes around these corners, some turbulence is created, resulting in this type of murmur. As the baby grows and becomes bigger from front to back, the main branch lung vessels do not take such a sharp turn to the lungs. Also, the lung themselves get larger. This type of murmur typically disappears when the baby reaches 6 to 9 months of age.
Innocent Flow Murmur
Normal blood flow across the aortic valve and pulmonary valve can be heard in some children and young adults. Children have thinner chest walls, which allows sounds to be more readily heard. This may be normal blood flow through a normal heart valve. These murmurs can be more pronounced if a child or adolescent is anemic or has a fever.
This murmur was named after Sir George Frederic Still, who is considered to be the “father of British pediatrics.” This type of murmur is most commonly heard in children between 3 and 6 years old, but is sometimes heard in infants and older children. It has a very characteristic sound that is often described as “musical,” “vibratory” or “twangy.” It can become louder when a child is ill, has a fever, or is anemic. This murmur typically resolves by the time a child is 10 to 12 years old, but some children may continue to have it later into life.
Sometimes blood flow returning from the head and arms through the large veins in the upper chest can be heard. This murmur will commonly disappear if the child’s head is turned to one side or the other. Applying gentle pressure to one side of the neck may also cause this murmur to disappear.
Blood flow in the arteries supplying blood to developing breast tissue in teenage girls may also be heard.
Abnormal, or pathologic, heart murmurs are heard in infants and children with structural abnormalities. These abnormal structures cause blood to flow turbulently and produce a murmur.
Valve Narrowing (Stenosis)
If a heart valve is too narrow, blood speeds up as it passes through and becomes turbulent, causing a murmur. This is much like when you put your thumb over the end of a garden hose. The more your thumb blocks the flow, the more loudly the water exits the end of the hose. If an outlet valve (pulmonary or aortic) is stenotic, the murmur may be accompanied by an extra heart sound called a valve click.
Outflow valve murmurs occur when the heart is squeezing (systole).
Inflow valve (tricuspid or mitral) narrowing creates a murmur when blood is entering the lower pumping chambers through these valves. This happens when the heart is relaxing (diastole).
Valve Leakage (Insufficiency/Regurgitation)
Leakage of the outflow valves (pulmonary or aortic) can create a murmur when the valve is supposed to be closed (diastole). Sometimes a leaky pulmonary valve is not easily heard because the pressures around this valve are relatively low. Leakage of the inflow valves (mitral or tricuspid) results when these valves are supposed to be closed – when the heart is squeezing blood out to the lungs and the body. Therefore, leakage of these valves causes a systolic murmur. Again, since the pressure around the tricuspid valve is typically low, leakage of this valve may not be easily heard.
Vessel/Outflow Tract Narrowing (Stenosis)
Narrowing in the lung vessels or aorta can result in an abnormal systolic murmur. Similarly, if there is muscular narrowing that prevents blood from leaving the pumping chambers, this can cause a murmur. Sometimes narrowing in the arteries supplying the kidneys can be heard in the abdomen.
Holes Between Walls of Heart Chambers (Septal Defects)
- Ventricular Septal Defects (VSDs): If a hole exists between the wall (the ventricular septum) that separates the heart’s lower pumping chambers (the ventricles), a murmur can be created when the heart squeezes (systole). Blood can exit the left ventricle normally through the aortic valve, but some may cross through this hole. If a lot of blood passes through this hole to the lungs, the extra blood returns to the heart after passing through the lungs. This extra blood passes through the normal mitral valve and may cause a diastolic murmur called a rumble.
You can learn more about ventricular septal defects and how they are treated here.
- Atrial Septal Defects (ASDs): Blood flow through a hole in the wall between the upper chambers of the heart (the atria) does not create a murmur as it passes from the left atrium to the right atrium. Instead, the extra blood that passes through this hole goes to the right ventricle. As it is pumped through a normal pulmonary valve, the extra blood volume may create a murmur.
You can learn more about atrial septal defects and how they are treated here.
- Continuous Murmurs: The most common example of a continuous murmur is a Persistent (or Patent) Ductus Arteriosus (PDA). Since this vessel (the PDA) connects the two large vessels that leave the heart and does not have a valve, blood flow occurs throughout the cardiac cycle, both in when the heart is squeezing (systole) and when it is relaxing (diastole). A continuous murmur can also be heard in some kinds of vascular malformations within the liver and the head. Some coronary artery abnormalities (coronary fistulae) may also result in a continuous murmur.
You can learn more about Persistent (or Patent) Ductus Arteriosus (PDA) and how it may be treated here.
If your child has a heart murmur, his or her doctor will determine if the murmur is innocent or abnormal. You can learn more about how this determination is made here.