The sounds of a beating heart are generated by the closing of its four valves, creating vibrations that travel through the chest wall. Listening to these sounds with a stethoscope, a practice known as auscultation, is a fundamental technique for assessing cardiac health. The two primary sounds are the familiar “lub-dub,” clinically termed S1 and S2, which correspond to the closure of two different sets of valves. Systematically listening to specific areas of the chest allows a healthcare professional to determine if the valves are functioning correctly and if blood flow is turbulent or smooth, detecting subtle changes that may signal underlying heart conditions.
Anatomical Context for Listening
The area of the chest that overlies the heart is called the precordium, extending roughly from the second to the fifth intercostal space on the left side of the sternum. To locate the specific listening areas, chest wall landmarks, such as the sternum and intercostal spaces, are used as standardized reference points. Finding the second intercostal space is typically the starting point, as it is located just below the bony ridge where the manubrium and the body of the sternum join, known as the sternal angle.
The locations where heart sounds are best heard do not exactly match the physical position of the heart valves within the chest. Instead, the sounds are carried or “radiated” by the blood flow to specific points on the chest wall where they are clearest and loudest. Standardizing these auscultation points ensures that examinations are consistent and that any variations in sound are reliably detected.
The Four Primary Auscultation Points
The systematic approach to cardiac auscultation involves listening over four main areas, each named for the valve whose sound is most prominent there. The aortic area is found at the second intercostal space just to the right of the sternal border. This location provides the clearest sound of the aortic valve closing, a component of the S2 sound.
Moving across the sternum, the pulmonic area is located at the second intercostal space along the left sternal border. At this site, the closure of the pulmonic valve, the second component of the S2 sound, is most clearly audible. These two upper sites are often collectively referred to as the “base” of the heart.
The tricuspid area is located lower on the chest, typically at the fourth or fifth intercostal space along the lower left sternal border. The sound heard here originates primarily from the closure of the tricuspid valve, which contributes to the S1 sound.
The mitral area, also known as the apex, is positioned near the heart’s point of maximal impulse. This site is located at the fifth intercostal space, moving inward toward the midline from the middle of the left clavicle. Here, the closure of the mitral valve, the loudest part of the S1 sound, is heard most distinctly.
Listening to these four specific points in sequence allows for a comprehensive assessment of all four heart valves. These four points form the foundation of cardiac auscultation, although other areas, like Erb’s point, are sometimes included.
Distinguishing Normal Heart Sounds
The first heart sound, S1, is the “lub” sound, marking the beginning of ventricular contraction (systole). This sound is generated by the simultaneous closure of the two atrioventricular (AV) valves: the mitral and the tricuspid valves. Although the mitral valve closes slightly before the tricuspid valve, S1 is usually heard as a single, combined sound.
The S1 sound is heard most loudly over the mitral and tricuspid auscultation areas. The second heart sound, S2, is the “dub” sound, which signals the end of systole and the beginning of the heart’s filling phase (diastole). It is caused by the closure of the two semilunar valves: the aortic and the pulmonic valves.
Unlike S1, the S2 sound is often physiologically split, meaning the aortic valve (A2) closes slightly before the pulmonic valve (P2). This subtle, two-part sound is heard most clearly at the base of the heart, specifically over the aortic and pulmonic areas. Differentiating between S1 and S2 at each listening point provides information about the timing and relationship of the sounds, helping determine if the heart’s rhythm and valve function are normal.