When the heart beats, it generates distinct sounds, often described as the familiar “lub-dub.” These noises result from the four heart valves snapping shut to prevent the backward flow of blood, not the heart muscle contracting. Listening to these sounds, known as auscultation, is a fundamental diagnostic method used to assess the function of the heart’s valves and chambers. By systematically placing a stethoscope on specific spots on the chest wall, medical professionals gather important auditory data about the cardiovascular system.
The Four Primary Auscultation Sites
To effectively listen to the heart, the chest wall is divided into four primary auscultation areas. Each area corresponds to where the sound from a specific valve is best projected and loudest. The systematic approach begins with the base of the heart and moves toward the apex.
The Aortic Area is located on the right side of the chest, specifically at the second intercostal space next to the sternum. Sounds from the aortic valve, which controls blood flow from the left ventricle into the aorta, are most clearly heard here. Moving directly across the sternum to the second intercostal space on the left side locates the Pulmonic Area. This site best appreciates the closure of the pulmonic valve, which regulates blood leaving the right ventricle.
The next listening point is the Tricuspid Area, situated lower on the left side of the sternum, usually around the fourth or fifth intercostal space. This location provides the clearest acoustic window for the tricuspid valve, which lies between the right atrium and the right ventricle. Finally, the Mitral Area, often called the apex of the heart, is found at the fifth intercostal space along the midclavicular line. This spot is the point of maximal impulse (PMI) and is where the sound of the mitral valve closing is most prominent.
Understanding Why Sound Travels
The heart valves are positioned deep within the mediastinum, yet the sounds they produce are audible at specific, distant points on the chest wall. This occurs because the vibrations created by the snapping shut of the valves travel through the blood and surrounding tissues. The turbulence and reverberation within the blood are the actual sources of the audible sound.
The locations where the stethoscope is placed correspond to the pathways along which the sound waves are most clearly transmitted to the surface. The sounds tend to radiate in the direction of blood flow as it exits the chamber, explaining why the best listening points are often slightly downstream from the valves. For instance, the sound of the aortic valve is carried up and to the right, following the path of the aorta. This projection allows a focused assessment of each valve without placing the stethoscope directly over the valve’s deep anatomical position.
Optimizing Sound Capture Through Patient Positioning
While the four primary sites provide a baseline assessment, altering the patient’s physical position can significantly enhance the audibility of fainter or more complex heart sounds. These changes in posture shift the heart’s relationship to the chest wall, bringing certain structures closer to the surface.
One common maneuver involves having the patient sit upright and lean slightly forward. This position is particularly useful for bringing the base of the heart closer to the stethoscope, which can amplify high-pitched diastolic murmurs, such as those related to aortic valve insufficiency. The patient is often asked to hold their breath in full expiration during this technique to minimize sound interference from the lungs.
Another technique is the left lateral decubitus position, where the patient lies on their left side. Lying on the left side rotates the heart within the chest cavity, bringing the apex nearer to the chest wall. This position is crucial for detecting low-frequency sounds, such as a third (S3) or fourth (S4) heart sound, and the diastolic rumble associated with mitral stenosis. Additionally, asking the patient to take a deep breath can differentiate between sounds, as increased venous return during inspiration often makes right-sided heart murmurs distinctly louder.