The rhythmic sounds of the heart are often described as a “lub-dub.” These two primary sounds, S1 and S2, are fundamental indicators of basic heart function. They are produced by the opening and closing of the heart’s four valves, which ensure blood flows efficiently through the circulatory system. Understanding these sounds offers insight into the heart’s mechanical actions.
Understanding the “Lub-Dub” Sounds
The first heart sound, S1, creates the “lub” and signifies the beginning of ventricular systole, when the heart’s lower chambers contract to pump blood. This sound results from the simultaneous closure of the tricuspid and mitral valves. These valves, located between the atria and ventricles, prevent blood from flowing backward into the upper chambers as the ventricles contract.
Following S1, the second heart sound, S2, produces the “dub.” This sound marks the end of ventricular systole and the beginning of ventricular diastole, when the heart’s ventricles relax and fill with blood. S2 is caused by the closure of the aortic and pulmonic valves. These semilunar valves prevent blood from flowing back into the ventricles from the aorta and pulmonary artery after blood ejection.
Locating the Heart Sounds
To listen for S1 and S2, specific areas on the chest wall, known as auscultation points, are used. These locations are where valve sounds are best transmitted, rather than directly over the anatomical position of the valves themselves, due to how sound waves travel.
The aortic area is in the second intercostal space (between the ribs), right of the sternum. Here, the S2 sound, specifically its aortic component, is most clearly audible. The pulmonic area is in the second intercostal space, left of the sternum. This site is optimal for hearing the pulmonic component of the S2 sound.
The tricuspid area is at the left lower sternal border, around the fourth or fifth intercostal space. The S1 sound, particularly its tricuspid component, is best heard in this region. Further to the left, at the fifth intercostal space along the mid-clavicular line (an imaginary line drawn straight down from the middle of the collarbone), is the mitral area, also known as the cardiac apex. This location provides the clearest resonance for the S1 sound, specifically its mitral component, and is also where the point of maximal impulse (PMI) is often felt.
Tips for Listening Effectively
Listening for heart sounds requires a quiet environment to minimize external distractions. Ensuring the room is free from ambient noise, such as television or conversations, allows for better concentration on the subtle sounds of the heart. Proper patient positioning enhances audibility; listening with the patient lying flat, sitting upright, or in a left lateral decubitus position can bring the heart closer to the chest wall, making the sounds clearer.
When attempting to discern S1 and S2, it is helpful to focus on one sound at a time. For instance, concentrate solely on identifying the “lub” (S1) for several beats before shifting attention to the “dub” (S2). While a stethoscope is used for auscultation, the information regarding heart sounds is for educational purposes only. Any concerns about heart health should always be discussed with a qualified healthcare professional, as self-diagnosis based on listening to heart sounds is not recommended.