A heart murmur is an extra sound during the heartbeat cycle that’s made by blood moving through the heart and its valves. Heart murmurs may be normal (innocent) or abnormal. Many normal conditions may cause the blood to flow with turbulence, causing a murmur to be heard. These conditions don’t necessarily indicate something is abnormal, nor do they cause an ill effect on the child’s health.
Normal heart murmurs
Among the conditions that may cause a normal heart murmur include the following:
- Physiologic peripheral pulmonary stenosis (PPS) – This type of heart murmur is typically heard in babies 1 to 2 months of age and tends to disappear at 6 to 9 months of age. These babies 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 heart murmur. As these babies grow and become bigger from front to back, the main branch lung vessels don’t take such a sharp turn to the lungs. Also, the lung themselves get larger.
- Innocent flow murmur – Normal blood flow across the aortic and pulmonary valves can be heard in some children and young adults. Children have thinner chest walls, making sounds 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 has a fever or anemia.
- Still’s murmur – This type of heart murmur was named after Sir George Frederic Still, considered the “father of British pediatrics.” This type of heart murmur is most commonly heard in children between 3 and 6 years old, but it’s sometimes heard in infants and older children. It has a very characteristic sound that’s often described as “musical,” “vibratory,” or “twangy.” It can become louder when a child is ill, has a fever, or is anemic. This heart murmur typically resolves when a child is 10 to 12 years old, but some children may continue to have it later in life.
- Venous hum – Sometimes, the blood flow returning from the head and arms through the large veins in the upper chest can be heard. This type of heart 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 heart murmur to disappear.
- Mammary soufflé – This type of heart murmur occurs in teenage girls (assigned female at birth) and occurs when blood flow in the arteries supplying blood to developing breast tissue may also be heard.
Abnormal heart murmurs
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 heart murmur.
- Valve narrowing (stenosis) – If a heart valve is too narrow, blood speeds up as it passes through and becomes turbulent, causing a heart 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 murmurs occur when an inflow valve is narrowing (tricuspid or mitral). Inflow murmurs typically occur when the heart is filling (diastole).
- Valve leakage (insufficiency/regurgitation) – Leakage of the outflow valves (pulmonary or aortic) can create a heart murmur when the valve is supposed to be closed (diastole). Sometimes, a leaky pulmonary valve isn’t 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 squeezes blood out to the lungs and the body. Therefore, leakage of these valves causes a systolic heart murmur. Similar to the pulmonary valve, pressure around the tricuspid valve is typically low, so 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 heart murmur. Similarly, if there’s muscular narrowing that prevents blood from leaving the pumping chambers, this can cause a heart murmur. Sometimes, narrowing in the arteries supplying the kidneys can be heard in the abdomen.
- Holes between walls of the 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 heart 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. The smaller the hole, the larger the murmur typically is.
- Atrial septal defects (ASDs) – Blood flow through a hole in the wall between the heart's upper chambers (the atria) doesn’t create a heart murmur as it passes from the left to the right atrium. Instead, the extra blood that passes through this hole goes to the right ventricle. The extra blood volume may create a heart murmur as the extra blood is pumped through a normal pulmonary valve. These murmurs may not be noted until adolescence.
- Continuous murmurs – The most common example of a continuous murmur is a patent ductus arteriosus (PDA). Since this vessel (the PDA) connects the two large vessels that leave the heart and doesn’t have a valve, blood flow occurs throughout the cardiac cycle, both when the heart is squeezing (systole) and when it’s filling (diastole). A continuous murmur can also be heard in vascular malformations within the liver and the head. Some coronary artery abnormalities (coronary fistulae) may also result in a continuous murmur.
Children's Heart Health
Information for parents of children with pediatric heart conditions. Read more about conditions, tests, and treatments for congenital heart disease.
Harper O'Bomsawin Toddler on the Run
Harper O'Bomsawin had a heart murmur, and with the care of a pediatric interventional cardiologist, an electrocardiogram identified she had coarctation of the aorta.