A heart murmur is a common finding in childhood, and Still’s murmur is the most frequently heard type, often affecting up to one-third of all children. This sound is classified as an “innocent” or “functional” murmur, meaning it is a harmless sound produced by the normal flow of blood through a structurally healthy heart. The presence of a Still’s murmur does not indicate any underlying heart defect or disease. Parents should be reassured that this benign finding requires no treatment or lifestyle changes.
Defining the Innocent Still’s Murmur
A heart murmur is an extra sound heard between the normal “lub-dub” heart sounds, caused by blood flowing turbulently. The Still’s murmur is thought to be generated by the rapid movement of blood through the left ventricular outflow tract, or potentially by the vibration of “false tendons” within the left ventricle. This rapid flow creates a sound that is distinctively musical or vibratory, sometimes compared to the sound of a tense string being plucked.
It is a soft, low-pitched sound that is heard best at the lower left edge of the breastbone. The sound is a “midsystolic crescendo-decrescendo” murmur, meaning it gets louder and then softer during the heart’s contraction phase.
The murmur is most often detected when a child is between the ages of two and seven years old. This sound may become noticeably louder when the child has an increased heart rate, such as during a fever, excitement, or after physical activity. It is also often loudest when the child is lying flat on their back.
The Expected Timeline for Resolution
A Still’s murmur almost always resolves on its own. While it is most commonly found in preschool and early school-aged children, the murmur tends to fade and eventually vanishes completely.
The typical timeframe for complete resolution is by adolescence or young adulthood. It requires no medical intervention, such as medication or surgery, to resolve.
The timeline is variable, and the murmur may not be present at every check-up, often seeming to “come and go” before it fully disappears. This variation in audibility is normal and can be influenced by the child’s body position or overall state of health at the time of examination.
The presence of the murmur into later childhood should not be a source of worry. The heart, which is structurally normal, simply outgrows the conditions that create the audible vibrations as the child matures. For the vast majority of children, the sound is completely gone before they reach their adult years.
Key Differences Between Innocent and Pathological Murmurs
Still’s murmur is differentiated from a pathological murmur by its qualities. The musical, vibratory, and soft nature of Still’s murmur indicates its innocence. A pathological murmur, by contrast, is often described as harsh or loud, and may be heard in a wider area of the chest or radiate to the neck or back.
The timing is another differentiator. Pathological murmurs are sometimes holosystolic or diastolic, meaning they last throughout the entire heart contraction or occur during the relaxation phase. A Still’s murmur causes no symptoms at all, which is a significant distinction.
A pathological murmur may be accompanied by noticeable signs of a heart problem, such as shortness of breath, unexplained fainting, or difficulty gaining weight, particularly in infants. If a doctor has any doubt about the nature of the sound, they may recommend a referral to a pediatric cardiologist for further evaluation.
Diagnostic tools such as an echocardiogram (an ultrasound of the heart) or an electrocardiogram (EKG) may be used to confirm that the heart is structurally normal. A Still’s murmur is ultimately a diagnosis of exclusion. This diagnosis is confirmed when the characteristic sound is present alongside a complete absence of other signs of heart disease.