The heart produces distinct, rhythmic sounds generated by the mechanical movement of its structures, primarily the opening and closing of its four valves. Listening to these sounds provides medical professionals with a non-invasive way to gain insight into the health of the heart muscle, the integrity of its valves, and the direction of blood flow. Changes in the rhythm, intensity, or presence of extra sounds can suggest various underlying conditions. Understanding these normal and abnormal heart sounds is foundational to interpreting cardiac health.
The Physiology of Normal Heart Sounds (S1 and S2)
The most recognizable heart sounds are the two primary components, S1 and S2, which create the familiar “Lubb-Dupp” rhythm. These sounds mark the beginning and end of the ventricular contraction phase, known as systole. Both sounds originate from the abrupt deceleration of blood caused by the closure of heart valves, not the opening of the valves.
The first heart sound, S1, corresponds to the “Lubb” and signals the beginning of systole. It is produced by the simultaneous closing of the atrioventricular (AV) valves (mitral and tricuspid valves). This closure prevents blood from flowing backward into the atria as the ventricles build pressure to eject blood.
The second heart sound, S2, the “Dupp,” marks the end of systole and the beginning of diastole. It is caused by the closure of the two semilunar valves (aortic and pulmonary valves) as blood attempts to flow back into the relaxed ventricles. S2 can sometimes split into two distinct components, especially during inspiration, because the aortic valve closes slightly before the pulmonary valve.
Accessory Sounds (S3 and S4)
Additional sounds, known as S3 and S4, are often referred to as gallops due to the three-beat rhythm they create. These sounds are not generated by valve closure but by the dynamics of blood filling the ventricles during diastole. They are typically lower in pitch than S1 or S2.
The third heart sound, S3, occurs early in diastole during the rapid filling phase. In children, young adults, or highly trained athletes, S3 can be a normal finding suggesting a pliable ventricular wall. In older adults, however, S3 often suggests ventricular volume overload, frequently associated with conditions like systolic heart failure.
The fourth heart sound, S4, occurs late in diastole, just before S1. It is caused by the forceful contraction of the atria pushing blood into a stiff or non-compliant ventricle. S4 is almost always pathological, often involving a thickened or less flexible ventricle caused by conditions such as systemic hypertension or severe aortic stenosis.
Identifying Heart Murmurs
Heart murmurs are distinct sounds—a swishing, whooshing, or rasping noise—that differ significantly from the crisp sounds of S1 and S2. A murmur is the audible manifestation of turbulent blood flow, which occurs when blood does not move smoothly through the heart’s chambers or valves. While normal blood flow is silent, any disruption creates detectable vibrations.
Murmurs arise primarily from two types of structural valve problems: stenosis and regurgitation. Stenosis occurs when a heart valve becomes stiff or narrowed, forcing blood to squeeze through a smaller opening, which increases the velocity and turbulence of the flow. Conversely, regurgitation, also called insufficiency, happens when a valve fails to close completely, allowing blood to leak backward into the preceding chamber.
Not all murmurs signify disease; some are “innocent” or “functional” and are common in children or during temporary states like fever or pregnancy. Pathological murmurs are categorized based on their timing within the cardiac cycle (systole or diastole). They are also graded on an intensity scale from one to six, where a higher grade indicates a louder sound and a potentially more significant flow disturbance.
How Heart Sounds Inform Diagnosis
Auscultation, the process of listening to heart sounds, serves as a valuable, non-invasive screening method in clinical practice. A physician uses the precise qualities of the sounds—timing, pitch, intensity, and location on the chest—to localize a potential problem. For example, a sound loudest at the apex may point toward a mitral valve disorder, while a sound near the sternum may implicate the aortic or pulmonary valves.
The timing of a murmur is particularly informative. A systolic murmur suggests a problem with flow during ventricular contraction, such as aortic stenosis or mitral regurgitation. Conversely, a diastolic murmur points toward issues during ventricular filling, potentially indicating aortic regurgitation or mitral stenosis.
While auscultation is a powerful diagnostic aid, heart sounds rarely provide a definitive diagnosis alone. They serve as crucial indicators that determine the necessity of further, more precise testing. The presence of an abnormal sound often prompts the use of imaging (such as an echocardiogram) or electrical monitoring (like an electrocardiogram) to confirm the structural or functional abnormalities suggested by the sounds.