A heart murmur is an unusual sound heard during the cardiac cycle, often described as a whooshing, blowing, or swishing noise. This sound differs from the typical “lub-dub” of the heart, which represents the closing of the heart valves. A murmur is a physical finding indicating turbulent blood flow within or near the heart. This finding requires evaluation to determine its cause, which may range from a temporary, harmless flow pattern to an underlying structural issue.
Understanding the Mechanism of a Heart Murmur
The sound of a heart murmur results from blood becoming turbulent as it flows through the heart’s chambers, valves, or major blood vessels. Normally, blood flows smoothly in a laminar fashion. When this movement is disrupted, it causes vibrations loud enough to be heard through a stethoscope.
Turbulence can be caused by blood flowing rapidly through a structurally normal heart, often seen during periods of high cardiac output like fever or intense exercise. The flow may also become turbulent when blood passes through a narrowed heart valve (stenosis). Alternatively, the sound occurs if a valve fails to close completely, allowing blood to leak backward (regurgitation or insufficiency).
Global Prevalence and Key Statistics
The prevalence of heart murmurs varies significantly between children and adults, largely due to the common occurrence of “innocent” murmurs in younger populations. A heart murmur is an extremely common finding during childhood, with estimates suggesting that up to 80% of children will have one detected at some point. Most of these childhood murmurs are innocent, meaning they are caused by normal blood flow dynamics and pose no threat to health.
In contrast, the prevalence of heart murmurs in the general adult population is lower but often carries greater potential for clinical significance. One study of adults aged 40 and older found a heart murmur detected in approximately 23% of participants upon auscultation. While many adult murmurs may be benign, they are more likely than those in children to be associated with an underlying structural heart condition, such as valvular heart disease.
The number of people with a pathological murmur, one caused by a structural heart defect, is substantially smaller. Congenital heart disease, which can cause a pathological murmur, is found in roughly one in every 100 children. Pathological murmurs in the general population are estimated to occur in less than 1% of individuals.
Distinguishing Innocent and Pathological Murmurs
Following the detection of a heart murmur, the primary step is determining whether it is an innocent (benign) or a pathological (abnormal) sound. This distinction relies on evaluating several specific clinical characteristics. Innocent murmurs are typically soft, described as musical or vibratory, and are heard only during the heart’s contraction phase (systole).
A key feature for differentiation is the timing of the sound; any murmur heard during the heart’s relaxation phase (diastole) is considered pathological until proven otherwise. Pathological murmurs also tend to be louder and harsher in quality, often graded as level three or higher on a scale of one to six. The location where the murmur is heard loudest, and whether the sound radiates to other areas like the neck or back, provides further clues about the underlying cause.
The presence of associated symptoms also suggests a pathological cause requiring intervention. While innocent murmurs do not cause symptoms, a pathological murmur may be accompanied by signs of decreased cardiac function. These symptoms can include shortness of breath, dizziness, chest pain, or episodes of syncope (temporary loss of consciousness).
Detection and Initial Diagnostic Steps
A heart murmur is first identified through auscultation, where a healthcare provider listens to the heart with a stethoscope. During this examination, the provider systematically listens to specific points on the chest to characterize the murmur’s timing, intensity, pitch, and location. This initial assessment guides the subsequent investigation.
If the initial physical examination and patient history raise suspicion of a pathological cause, further diagnostic testing is pursued. The non-invasive echocardiogram (echo) is the primary diagnostic tool used for evaluation. This test utilizes sound waves to create moving images of the heart’s structure, visualizing the chambers, valves, and the direction of blood flow.
The echocardiogram confirms if the murmur is caused by a structural issue, such as a leaky valve or a hole between chambers. An electrocardiogram (ECG) may also be performed to check the heart’s electrical activity and look for signs of chamber enlargement or rhythm abnormalities. These tests provide the objective data needed to determine the cause of the turbulent flow and establish a definitive diagnosis.