A heart murmur is an unusual sound, like a whoosh or swish, heard between heartbeats and caused by turbulent blood flow. In children, a common cause is a ventricular septal defect (VSD), a congenital heart defect. A VSD is a hole in the septum, the wall separating the heart’s two lower chambers (ventricles), which allows blood to pass from the left to the right side of the heart.
What a VSD Murmur Sounds Like
The sound of a VSD murmur results from blood flowing through the hole in the ventricular septum. The pressure inside the left ventricle is much higher than in the right. This pressure difference forces blood to jet from the left chamber into the right, creating a distinct noise. This turbulence is comparable to water forced at high pressure through a narrow garden hose nozzle.
A physician using a stethoscope hears this murmur at the lower left sternal border, the area to the left of the breastbone. The sound is often described as harsh and high-pitched. The murmur is classified as “holosystolic” or “pansystolic,” a medical term meaning the sound is continuous. It begins with the first heart sound (“lub”) and continues to the second heart sound (“dub”) without a pause.
This continuous sound occurs because the pressure in the left ventricle remains higher than in the right throughout the heart’s contraction phase (systole). This persistent pressure gradient ensures blood flows through the defect for the full duration between the “lub” and “dub” sounds. For some small defects, the murmur may be shorter if the hole seals itself off during late systole.
What the Sound Reveals About the VSD
The loudness of a VSD murmur often has an inverse relationship with the size of the hole. A loud, harsh murmur is frequently a sign of a small, restrictive VSD. The sound is generated by a large pressure difference forcing blood through a small opening. This high-velocity jet creates significant turbulence and a prominent murmur.
These smaller defects are often less concerning medically. The small hole limits the amount of blood passing from the left to the right ventricle. Because the volume of shunted blood is low, the heart and lungs are not overworked. Many of these small VSDs close on their own without medical intervention.
Conversely, a softer or absent murmur may indicate a larger VSD. With a large defect, the pressures between the ventricles start to equalize. When the pressure gradient is lower, blood flows through the opening with less force, generating a quieter sound. A large VSD that allows significant blood to be shunted can strain the heart and increase blood flow to the lungs, a more serious situation requiring careful monitoring.
The Diagnostic Process
Diagnosing a VSD often begins when a doctor detects a heart murmur during a routine physical exam. The murmur is a clinical sign pointing toward a possible issue, but it is not a diagnosis itself. The sound’s characteristics, such as its timing, loudness, and location, help the physician determine the likely cause.
If a VSD is suspected, the next step is a referral to a pediatric cardiologist. The definitive diagnostic tool is an echocardiogram, a non-invasive procedure using ultrasound waves. It creates detailed, moving images of the heart’s structure and function.
The echocardiogram allows the cardiologist to visualize the hole in the ventricular septum. It provides precise information about the VSD’s size, location, and the direction of blood flow. The imaging also assesses the impact on the heart, showing if chambers are enlarged or the muscle is strained. This assessment helps determine the appropriate management.
When a VSD Murmur Disappears
Many VSDs close spontaneously without medical intervention, most commonly during infancy and early childhood. As the hole shrinks, the sound of the murmur changes. This provides an audible sign that the condition is improving.
As a VSD gets smaller, the opening becomes more restrictive, causing the murmur to become higher in pitch or shorter in duration. The sound diminishes until the hole closes completely. At this point, the murmur disappears entirely, confirming the defect has sealed.
The disappearance of the murmur means the abnormal blood flow pathway is gone. The heart is no longer subjected to inefficient shunting of blood, allowing it to pump more effectively. For many children, the fading of their VSD murmur is a reassuring sign of a complete recovery.