The heart produces rhythmic sounds as it pumps blood throughout the body. These noises, often described as a “lub-dub,” arise from the mechanical actions of the heart’s valves opening and closing. Listening to these sounds provides a non-invasive way to gain insights into cardiac function. Understanding where to place a listening device on the chest is the initial step in appreciating these internal body rhythms.
Tools and Techniques for Listening
To listen for heart sounds, a stethoscope is the instrument used. Acoustic stethoscopes, the most common type, feature a chest piece, tubing, and earpieces that transmit body sounds. The chest piece has two sides: a diaphragm, a flat plastic disc for higher-frequency sounds, and a bell, a hollow cup for lower-frequency sounds. Electronic stethoscopes are also available, which amplify and filter sounds, offering clearer audio, especially in noisy environments.
For effective listening, the environment should be quiet. The patient should be in a relaxed position, either lying down or sitting upright. Placing the stethoscope directly on the bare skin of the chest ensures the best sound transmission, avoiding muffling from clothing. Applying appropriate pressure with the stethoscope’s chest piece, firm for the diaphragm and light for the bell, helps optimize the sounds heard.
Specific Locations for Auscultation
Listening to heart sounds, known as auscultation, is performed over four primary areas on the chest. These spots are not necessarily directly over the heart valves themselves but are where the sounds project most clearly due to blood flow and surrounding structures. These locations are referred to as cardiac landmarks.
The aortic area is in the second intercostal space (the space between the second and third ribs) just to the right of the sternum (breastbone). Aortic valve sounds are best heard here. Moving to the second intercostal space just to the left of the sternum identifies the pulmonic area, where pulmonic valve sounds are most audible.
The tricuspid area is at the fourth or fifth intercostal space along the lower left sternal border. Sounds from the tricuspid valve are clearest here. The mitral area, also known as the apex, is found at the fifth intercostal space on the left side, medial to the midclavicular line (an imaginary line running down from the middle of the collarbone). Mitral valve sounds are best heard at this location.
Understanding Normal Heart Sounds
The common “lub-dub” sound consists of two distinct components, S1 and S2. These sounds are produced by vibrations created when the heart valves close, causing changes in blood flow and tensioning of cardiac structures. The timing and characteristics of these sounds reflect the heart’s normal pumping cycle.
The first heart sound, S1, is the “lub” noise and marks the beginning of ventricular contraction, known as systole. This sound is primarily caused by the simultaneous closure of the mitral and tricuspid valves, which separate the atria from the ventricles. The mitral valve’s closure is typically the louder component of S1.
The second heart sound, S2, is the “dub” noise and signals the end of systole and the beginning of ventricular relaxation, or diastole. S2 is generated by the closure of the aortic and pulmonic valves, which are the semilunar valves leading out of the ventricles. The aortic valve normally closes slightly before the pulmonic valve, creating two components (A2 and P2) that can sometimes be heard separately, especially during inspiration.