The medical practice of listening to the heart, known as cardiac auscultation, is a fundamental, non-invasive method for assessing cardiovascular health. This technique involves using a simple instrument, the stethoscope, to detect and interpret the complex sounds generated by the beating heart and flowing blood. By carefully listening to these internal vibrations, a healthcare provider can gain immediate insight into the function of the heart’s valves and muscle chambers. Auscultation serves as an initial diagnostic tool that can quickly identify potential abnormalities, guiding the need for more advanced testing.
The Stethoscope and the Technique of Auscultation
The stethoscope is an acoustic device designed to amplify and transmit internal body sounds to the listener’s ears. Its chest piece typically features two sides: the diaphragm and the bell, each engineered to capture different sound frequencies. The diaphragm is the larger, flat side used to detect high-frequency sounds, including normal heart and most lung sounds. Applying firm pressure with the diaphragm against the skin filters out lower frequencies and properly transmits the higher-pitched sounds. Correct placement of the earpieces, which should point forward toward the nose, ensures the sound is directed properly into the ear canals.
The bell is the smaller, concave side, designed to capture low-frequency sounds. These lower-pitched sounds include certain abnormal heart sounds, such as gallops. To optimize the detection of these sounds, the bell must be placed lightly on the skin. Excessive pressure with the bell can cause the skin to act like a diaphragm, filtering out the low-pitched sounds. Auscultation requires a quiet environment, as heart sounds are often faint and easily obscured by ambient noise.
Mapping the Heart: Where to Listen
Listening to the heart is a systematic survey of four specific areas on the chest wall, known as the auscultation points. These points are not directly over the anatomical location of the heart valves but are the sites where the sound produced by each valve is best projected and heard.
The Four Auscultation Points
- The Aortic Area is located at the second intercostal space just to the right of the sternum, providing the clearest sound transmission from the aortic valve.
- The Pulmonic Area is found at the second intercostal space just to the left of the sternum, where the pulmonic valve sounds are best heard.
- The Tricuspid Area is typically found along the lower left sternal border, allowing for the assessment of the tricuspid valve.
- The Mitral Area, often referred to as the apex, is situated at the fifth intercostal space in the midclavicular line, where the closure of the mitral valve is heard most distinctly.
Decoding the Heartbeat: Normal Sounds
A normal, healthy heartbeat produces two distinct sounds commonly described as “lub-dub,” which medical professionals refer to as the first (S1) and second (S2) heart sounds. These sounds are not caused by the heart muscle contracting but by the sudden closure of the heart’s four valves, which creates turbulence and vibration in the blood and cardiac structures. The timing and clarity of these two sounds define the normal cardiac cycle.
The first sound, S1, marks the beginning of the ventricular contraction phase, known as systole. This sound is generated by the closure of the two atrioventricular valves (mitral and tricuspid) as pressure rises in the ventricles. Although the mitral valve component usually precedes the tricuspid component, the sound is typically perceived as a single, unified sound.
The second sound, S2, signals the end of systole and the beginning of the ventricular relaxation phase, diastole. S2 is produced by the closure of the two semilunar valves (aortic and pulmonic). The aortic valve normally closes slightly before the pulmonic valve, a difference often accentuated during inspiration when increased blood flow delays the pulmonic valve closure. The silence between S1 and S2 is systole (ventricular contraction), while the longer silence between S2 and the next S1 is diastole (ventricular filling).
When Sounds Signal a Problem
While S1 and S2 are the normal heart sounds, the presence of additional or altered sounds can alert a practitioner to a potential cardiac issue. These abnormal sounds often indicate turbulent blood flow or structural problems within the heart. Recognizing these deviations from the normal pattern is a significant aspect of auscultation.
One of the most common abnormal findings is a heart murmur, a whooshing or swishing sound that is longer than the brief, sharp S1 and S2 sounds. Murmurs are caused by turbulent blood flow, which may result from blood leaking backward through an incompetent valve or flowing forward through a narrowed, stiff valve. The timing of the murmur—whether it occurs during systole or diastole—helps pinpoint the specific valve or structural defect responsible.
Other pathological sounds include gallops, referred to as S3 and S4. The third heart sound (S3) occurs early in diastole and is caused by rapid filling into a stiff or volume-overloaded ventricle. While S3 can be a normal finding in children, its presence in older adults often suggests heart failure.
The fourth heart sound (S4) occurs just before S1 in late diastole and is associated with the vibration of a non-compliant, stiff ventricular wall as the atria contract. An S4 is a sign of a stiffened ventricle, often seen in conditions like ventricular hypertrophy. A pericardial friction rub is a high-pitched, scratching sound that may indicate inflammation of the pericardium, the sac surrounding the heart.