A heart murmur is an extra or unusual sound heard when a healthcare provider listens to the heart with a stethoscope. This sound, often described as a whooshing or swishing noise, is caused by turbulent blood flow within the heart or major blood vessels. The normal heartbeat makes two distinct sounds, “lub-dub,” representing the closing of the heart’s valves. A murmur occurs when disrupted blood flow creates a vibration. While many murmurs are harmless, their seriousness depends entirely on the underlying cause, necessitating a medical evaluation.
The Critical Distinction: Innocent vs. Abnormal Murmurs
The seriousness of a heart murmur is determined by classifying it as either “innocent” or “abnormal.” The majority of murmurs are innocent, sometimes called functional or physiologic murmurs. An innocent murmur is produced by a structurally normal heart and does not indicate any underlying disease or defect. This type of murmur poses no health risk, requires no medical treatment, and does not restrict physical activity.
In contrast, an abnormal or pathological murmur signifies that the turbulent blood flow results from a structural problem within the heart. These issues can involve the heart valves, the walls separating the chambers, or the large vessels connected to the heart. Abnormal murmurs require investigation because they signal a condition that may affect heart function. The characteristics of the sound, such as its timing, pitch, and location, help a physician differentiate between the two types.
Causes of Innocent Murmurs
Innocent murmurs occur when blood moves more rapidly than usual through the heart’s chambers and valves, temporarily increasing turbulence. This increased blood flow is often a response to a physiological state rather than a structural defect. Physical activity or strenuous exercise can temporarily elevate the heart rate and speed of blood circulation, leading to a detectable murmur that resolves quickly upon rest. Conditions that increase the body’s metabolic demand or alter the blood’s composition can also cause an innocent murmur.
Examples of conditions causing temporary innocent murmurs include:
- Fever, which raises the heart’s output as the body works to cool itself.
- Anemia, which reduces blood viscosity, allowing it to flow more quickly and turbulently.
- Hyperthyroidism, which accelerates the heart rate due to excessive hormone production.
- Pregnancy, as the heart must pump an increased volume of blood to support the fetus.
- Periods of rapid growth in children, as heart and vessel sizes change relative to each other.
Underlying Conditions That Cause Abnormal Murmurs
Abnormal murmurs are directly linked to structural defects that impede the heart’s ability to pump blood efficiently. The most common cause is heart valve disease, where the four valves become dysfunctional. These problems manifest primarily as either stenosis or regurgitation.
Stenosis refers to the narrowing or stiffening of a heart valve, forcing the heart to pump harder to push blood through a smaller opening. This restricted path causes significant turbulence. Regurgitation, or insufficiency, occurs when a valve does not close completely, allowing blood to leak backward into the preceding chamber. This backflow creates the characteristic swishing sound and reduces effective pumping.
Congenital heart defects, present from birth, are another primary cause. These often involve septal defects, which are “holes” in the walls separating the heart’s chambers, such as an atrial septal defect (ASD) or a ventricular septal defect (VSD). These holes allow blood to shunt, generating a high-velocity flow and a murmur. Cardiomyopathy, a disease of the heart muscle, can also lead to valve dysfunction and abnormal murmurs.
Diagnosis and Follow-Up
The diagnosis of a heart murmur begins with a careful physical examination using a stethoscope. The physician listens for specific characteristics, including the sound’s timing during the heartbeat, its pitch, and the exact location where it is loudest. Murmurs heard during the heart’s relaxation phase (diastole) are far more likely to be abnormal than those heard during the contraction phase (systole).
If the physical exam suggests a pathological murmur, further non-invasive tests are ordered to visualize the heart’s structure and function. An echocardiogram is the primary tool for identifying structural issues like valve stenosis, regurgitation, or septal defects, and it measures the heart’s pumping efficiency. An electrocardiogram (EKG) and a chest X-ray may also be performed to look for signs of strain on the heart.
For innocent murmurs, no treatment is necessary. Abnormal murmurs often require ongoing monitoring, medication to ease the heart’s workload, or surgical intervention to repair or replace a damaged valve or close a defect.