When a physician listens to a child’s heart and mentions an extra sound beyond the familiar “lub-dub,” parents often feel concern. This extra sound is called a heart murmur, a common finding in pediatric medicine. A heart murmur is simply the sound made by blood moving through the heart and surrounding vessels. Up to 80% of children will have a murmur detected, and the vast majority of these sounds are entirely harmless, indicating no underlying heart disease.
Understanding the Sound: What a Heart Murmur Actually Is
The normal heart sounds, “lub-dub,” are generated by the closing of the heart’s valves during precise, laminar blood flow. The “lub” (S1) is the sound of the mitral and tricuspid valves closing, and the “dub” (S2) is the sound of the aortic and pulmonic valves closing. A heart murmur is a distinct whooshing, swishing, or humming sound that occurs when blood flow becomes turbulent.
This turbulence is similar to the noise made by water rushing quickly through a narrow hose. Instead of moving smoothly, the blood swirls and vibrates as it passes through the heart’s chambers or valves. This chaotic flow generates the audible sound waves heard with a stethoscope. The intensity of this turbulence, and thus the loudness of the murmur, is affected by the speed and volume of blood flow.
The Crucial Distinction: Innocent Versus Abnormal Murmurs
The most important distinction a physician makes upon hearing a murmur is whether it is “innocent” or “abnormal” (pathologic). Innocent murmurs, also called functional or physiologic murmurs, are incredibly common, occurring in over two-thirds of school-aged children. These murmurs are not a sign of heart disease, and the child’s heart is structurally normal. They are typically caused by temporary conditions that increase the speed of blood flow, such as a fever, anemia, increased cardiac output during a growth spurt, or periods of excitement and anxiety.
Innocent murmurs are typically soft, change in intensity with body position, and do not radiate strongly to other areas of the body. They require no treatment, do not place any restrictions on a child’s activity, and often disappear entirely as the child grows older.
Abnormal murmurs, by contrast, are much rarer, occurring in less than 1% of the population. These sounds are generated by a problem with the heart’s structure, such as a defect in a valve or a hole between heart chambers.
Abnormal murmurs are generally louder, harsher, and may be heard throughout the entire heartbeat cycle, or only when the heart is relaxing. Unlike innocent murmurs, which are usually asymptomatic, a child with a pathologic murmur may show signs like poor feeding, shortness of breath, excessive sweating, or bluish discoloration of the lips or fingers. The presence of these associated symptoms or a distinct sound quality signals the need for further investigation to identify the structural cause.
Evaluating Abnormal Murmurs: Diagnosis and Underlying Causes
When a physician suspects an abnormal murmur, a thorough evaluation is initiated, beginning with a detailed assessment using a stethoscope, known as auscultation. The doctor listens carefully to the murmur’s specific characteristics, including its timing in the cardiac cycle (systolic, diastolic, or continuous), its pitch, and its intensity, which is graded on a scale from 1 (barely audible) to 6 (very loud). Features like a diastolic murmur or one that is Grade 4 or higher with a palpable vibration, known as a thrill, are strong indicators of a structural problem.
The definitive tool for evaluating the heart’s structure is the echocardiogram (echo), which uses sound waves to create a moving image of the heart and its blood flow. This non-invasive ultrasound allows a pediatric cardiologist to visualize the heart chambers, valves, and surrounding blood vessels to pinpoint the exact cause of the turbulent flow.
Common structural defects that cause abnormal murmurs in children are often congenital, meaning present at birth. These causes frequently involve “holes” in the heart, such as a Ventricular Septal Defect (VSD) or Atrial Septal Defect (ASD), which are openings in the walls separating the heart chambers. Other causes include Patent Ductus Arteriosus (PDA), where a blood vessel that is supposed to close after birth remains open, or valve problems like stenosis, which is a narrowing that restricts blood flow. The EKG, or electrocardiogram, may also be used to check the heart’s electrical activity and look for signs of chamber enlargement or strain.
Management and Outlook
The management plan and long-term outlook for a child with a heart murmur depend entirely on the type of murmur identified. For children with an innocent murmur, the prognosis is excellent, and no medical intervention is necessary. These children can participate in all normal activities and sports without restriction. The murmur is likely to disappear over time as the child grows, although even if it persists into adulthood, it remains a harmless finding.
If the murmur is determined to be abnormal and caused by a structural defect, the approach is tailored to the specific condition. For small defects, such as a tiny VSD, observation may be the plan, as some small holes can close spontaneously as the child gets older. Larger or more complex defects may require medication to manage symptoms or, in some cases, a surgical procedure or catheter-based intervention to repair the structural issue. Early identification and management of abnormal murmurs, especially those caused by congenital heart defects, often lead to a positive long-term outcome, allowing the child to live a full and active life.