Listening to heart sounds means placing a stethoscope at specific spots on the chest and recognizing the patterns you hear. The normal heart produces two distinct sounds per beat: a “lub” (called S1) and a “dub” (called S2). Learning where to listen, what equipment settings to use, and how to position the person being examined will help you hear these sounds clearly and catch anything unusual.
What Creates the Sounds
Heart sounds come from valves snapping shut as blood moves through the heart’s four chambers. S1, the first and lower-pitched sound, happens when the two valves between the upper and lower chambers close at the start of each squeeze. S2, the slightly higher-pitched sound, happens when the aortic valve and the pulmonary valve close after the heart finishes pushing blood out to the body and lungs.
S2 actually has two components. The aortic valve closes first, followed closely by the pulmonary valve. When you breathe in, the slight delay between these two closures widens, creating what’s called a “split” S2. This is normal. The aortic closure sound carries well across the entire chest, so when you hear S2 at almost any listening point, you’re primarily hearing that aortic component.
The Five Listening Points
There are five standard spots on the chest where heart sounds come through most clearly. Each corresponds to the direction blood flows from a specific valve, not the valve’s exact physical location. You can find the right rib spaces by starting at the top of the breastbone and counting down, feeling for the gaps between ribs.
- Aortic area: Right side of the breastbone, in the space between the second and third ribs.
- Pulmonic area: Left side of the breastbone, same level, between the second and third ribs.
- Erb’s point: Left side of the breastbone, one space lower, between the third and fourth ribs. This spot picks up sounds from both the aortic and pulmonary valves and is useful for catching certain murmurs.
- Tricuspid area: Lower left edge of the breastbone, between the fourth and fifth ribs.
- Mitral area: At the heart’s lowest tip, between the fifth and sixth ribs on the left side, roughly below the middle of the collarbone. This is where you place the stethoscope to hear mitral valve sounds most clearly.
A common approach is to work through these five points in order, spending enough time at each to hear several full heartbeat cycles. Research on heart sound recordings suggests you need at least six complete beats at each location to get a reliable assessment.
Using the Stethoscope Correctly
Most stethoscopes have two sides on the chest piece: a flat, wider side (the diaphragm) and a smaller, concave side (the bell). They filter sound differently, and switching between them is essential for a thorough exam.
The diaphragm works best for higher-pitched sounds. Press it firmly against the skin to hear S2 clearly, along with clicks and the soft, high-pitched murmur of a leaky aortic valve. The bell picks up low-pitched sounds when you rest it gently on the skin with minimal pressure. Use it to listen for the rumbling murmur of a narrowed mitral valve or the extra heart sounds (S3 and S4) that signal trouble. If you press the bell too hard, the skin underneath stretches tight and acts like a diaphragm, filtering out those low frequencies you’re trying to hear.
Some newer stethoscopes use a single-sided chest piece that switches between bell and diaphragm modes based on how firmly you press. Light pressure gives you the bell effect; firm pressure gives you the diaphragm effect.
Positioning Makes a Difference
The standard starting position is lying flat on the back, but certain sounds become much easier to hear with a change in posture.
Rolling onto the left side (left lateral decubitus position) brings the heart’s tip closer to the chest wall. This is the go-to position for hearing the low-pitched rumble of mitral stenosis and for detecting a faint S3. Place the bell lightly at the mitral area while the person lies in this position and you’ll often hear sounds that were inaudible moments earlier.
Sitting up and leaning forward pushes the base of the heart closer to the front of the chest. This position is ideal for hearing the soft, high-pitched murmur of aortic regurgitation. Ask the person to exhale and hold their breath briefly, which brings the heart even closer and eliminates breath sounds that can mask what you’re listening for. Sounds related to the sac surrounding the heart (the pericardium) are sometimes best heard with the person on hands and knees, though this position is rarely needed outside specific clinical scenarios.
Reducing Background Noise
Ambient noise is the biggest obstacle to hearing heart sounds clearly. A study examining how noise degrades heart sound recordings found that continuous background sounds, like conversation, television, or ventilation systems, are far more disruptive than brief, transient noises like a cough or a door closing. Clinicians rated ambient noise as more problematic than the patient’s own body sounds or movement.
Close windows, turn off televisions, and choose the quietest room available. Ask the person to breathe normally and stay still. If you’re recording sounds digitally, aim for longer recordings rather than short clips, since analysis accuracy drops significantly with brief samples.
What Extra Sounds Mean
Beyond the normal S1 and S2, two additional sounds are worth understanding.
S3 is a low-pitched sound that occurs just after S2, during the phase when blood rushes from the upper chambers into the lower chambers. It creates a rhythm that sounds like the word “Kentucky” (S1-S2-S3). In children and young adults, S3 is often normal and simply reflects a healthy, elastic heart. After age 40, an S3 usually signals that the heart’s lower chambers are overstretched or not pumping effectively. In people with heart failure, an S3 is associated with elevated pressures inside the heart and carries prognostic weight: it’s linked to higher risk of hospitalization and worse outcomes.
S4 is a low-pitched sound that occurs just before S1, producing a rhythm like “Tennessee” (S4-S1-S2). It happens when the upper chambers contract forcefully against stiff lower chambers that resist filling. A stiff ventricle wall, whether from thickening due to high blood pressure or from reduced blood supply, is the usual cause. S4 is almost always abnormal in adults and points to elevated filling pressures in the heart.
Both S3 and S4 are best heard with the bell of the stethoscope, using light pressure at the mitral area.
Recognizing Murmurs
Murmurs are whooshing or blowing sounds caused by turbulent blood flow through or near the heart valves. They vary widely in volume, and the Levine scale grades them from 1 to 6. A grade 1 murmur is so faint you might only catch it after several seconds of focused listening. A grade 2 is faint but recognizable immediately. Grade 3 is moderately loud, grade 4 is loud, and grade 5 is so loud you can hear it with only the edge of the stethoscope touching the skin. A grade 6 murmur can be heard without a stethoscope at all.
When you hear a murmur, note where in the heartbeat cycle it falls. Murmurs between S1 and S2 (systolic, during the heart’s squeeze) are common and often harmless. Murmurs between S2 and the next S1 (diastolic, during the heart’s relaxation phase) are more likely to indicate valve disease and always warrant further evaluation.
Digital Stethoscopes and AI Detection
Digital stethoscopes amplify heart sounds electronically, let you adjust frequency filtering, and can record audio for later review or sharing. Some now integrate AI algorithms trained to recognize patterns associated with valve disease.
A prospective study published in the European Heart Journal tested an AI-enabled digital stethoscope on 357 patients aged 50 and older who had risk factors for heart disease. The AI detected moderate to severe valve disease with 92.3% sensitivity, compared to 46.2% for a traditional stethoscope in the same patients. The tradeoff was a slight increase in false positives, but the researchers concluded this was justified by the dramatically better detection rate. These devices record high-fidelity sound and apply machine-learning algorithms to flag abnormal acoustic patterns, essentially giving a second opinion in real time.
For learners, digital stethoscopes offer a practical advantage: you can replay recordings, slow them down, and compare what you’re hearing against reference libraries. Several free apps and websites host libraries of normal and abnormal heart sounds recorded at each of the five standard listening points, which can accelerate the learning curve significantly.