You’re listening to a heartbeat through a stethoscope for the first time and someone says, “That’s S1, now wait for S2.Even so, ” Easy to say. Harder to actually hear Simple as that..
Most people learning cardiac auscultation get stuck on the same dumb thing: they’re not sure where on the chest they’re even supposed to put the bell or diaphragm. And honestly, that’s the part most guides get wrong. They jump straight into “lub-dub” sounds without telling you where the where is.
So let’s fix that. Here’s the real talk on where is S1 and S2 heard — not just in theory, but in practice, on an actual human chest Which is the point..
What Is S1 and S2
S1 and S2 are the two main heart sounds you hear on every normal cardiac cycle. S1 is the “lub.” It happens when the mitral and tricuspid valves snap shut at the start of systole. Here's the thing — s2 is the “dub. ” That’s the aortic and pulmonary valves closing at the end of systole.
Look, you don’t need the physiology lecture to find them. The chest is not a speaker. But you do need to know this: they’re not heard equally well everywhere. Different valves sit in different spots, and the sound they make travels best to specific areas Which is the point..
The basic sound map
Here’s the short version. S1 is loudest at the apex — that’s the bottom left of the chest, around the fifth intercostal space in the midclavicular line. S2 is loudest at the base — up near the second intercostal space, right and left of the sternum Less friction, more output..
That’s the headline. But if you stop there, you’ll miss a lot.
Why apex and base matter
The apex is where the mitral valve lives, more or less. So when S1 closes that valve, the noise lands hardest at the apex. The base is closer to the aortic and pulmonary valves, so S2 — which is those valves shutting — comes through clearest up there.
This is where a lot of people lose the thread.
Turns out, this split is the single most useful thing to remember when someone asks where is S1 and S2 heard.
Why It Matters
Why does this matter? Because most people skip it and then wonder why every heartbeat sounds like mush.
If you listen at the wrong spot, S1 and S2 can sound weirdly timed, faint, or even reversed. On top of that, a student once told me they thought a patient had a gallop because S2 sounded louder than S1 at the apex. On top of that, nope. They were just in the wrong place.
And in real clinical life, getting the locations right changes what you catch. A mitral stenosis murmur follows S1 at the apex. Think about it: an aortic regurgitation murmur follows S2 at the base, right sternal edge. If you don’t know where S1 and S2 are heard best, you’ll misplace the murmur too.
Worth knowing: confusing S1 and S2 is one of the top reasons beginners write down the wrong rhythm. It’s not just academic. It messes with your whole read of the heart And it works..
How It Works
Alright, the meaty part. How do you actually hear S1 and S2 in the right places?
Step one: position the person
Supine is fine to start. Left lateral decubitus makes the apex pop more if you’re struggling. Sit them up for base sounds if they’re breathy or obese — lung tissue muffles stuff.
Step two: find the landmarks
Don’t guess. Midclavicular line is halfway between sternum and nipple-ish on the left. Day to day, that fifth space there? That's why drop down to find the third, fourth, fifth. The second intercostal space is at the sternal angle. Think about it: count ribs. That’s your apex listen point.
Step three: use the right head
S1 and S2 are both low-ish frequency, but S1 has more low-end thump. And use the diaphragm pressed firm for S2 at the base — it cuts breath sounds. For S1 at the apex, the bell with light touch often shows it cleaner, especially in slower hearts Not complicated — just consistent..
Step four: listen at the classic spots
Here’s the practical map most people actually use:
- Aortic area — second right intercostal space. S2 is loud here.
- Pulmonary area — second left intercostal space. S2 also loud, sometimes split.
- Tricuspid area — fourth left intercostal space, sternal border. S1 decent here.
- Mitral area (apex) — fifth left intercostal, midclavicular. S1 loudest, period.
So when someone asks where is S1 and S2 heard, the honest answer is: S1 best at mitral/apex, S2 best at aortic and pulmonary/base.
Step five: compare side by side
Put your stethoscope at the apex. Hear lub-dub? Now move to the base. So hear dub-lub? No — you’ll hear dub as the louder one now. Even so, that contrast is your confirmation. S1 didn’t vanish. You just moved to where S2 wins.
Step six: use respiration
Here’s what most people miss. S2 splits on inhale at the pulmonary area. So listen there, ask them to breathe in. The “dub” becomes “dub-d-d.” That tells you you’re hearing S2 properly and you’re in the right zone The details matter here..
Common Mistakes
Honestly, this is the part most guides get wrong — they list spots but don’t say what goes sideways.
One: listening only at the apex and calling it a day. Think about it: you’ll never appreciate S2 properly that way. Base matters.
Two: pressing the bell too hard. Press and it becomes a diaphragm, killing the low S1 at the apex. Light touch, people Easy to understand, harder to ignore..
Three: counting interspaces wrong. Palpate the sternal angle. If you’re at the third space thinking it’s the second, your “base” is garbage. Always.
Four: confusing S1 and S2 because of tachycardia. And at 130 bpm, lub-dub-lub-dub blurs. On top of that, use the carotid pulse. Think about it: pulse = S1. That anchor never lies.
Five: ignoring body habitus. Now, in bigger chests, sounds shift. Apex might be lower, sixth space. Don’t trust the textbook line blindly — find the point of maximal impulse with your hand first.
Practical Tips
What actually works when you’re standing there with a cold stethoscope and a confused patient?
- Warm the bell. Cold metal makes them suck in air and wreck your listen.
- Find the PMI (point of maximal impulse) by palpation before auscultation. That’s your apex, no guessing.
- If S1 is soft, roll the patient left. It’s like turning up the volume.
- At the base, tell them to stop talking. Even whispering rides over S2.
- Practice on yourself. Your own S1 at apex is easy to learn. Then take it to real chests.
- Record a few normal cycles at each spot. Memory of “where is S1 and S2 heard” sticks only if your ear has been there.
And look — don’t obsess over perfect terminology. If you know apex = S1 town and base = S2 town, you’re ahead of most first-years Not complicated — just consistent. And it works..
FAQ
Where is S1 heard best? At the apex, fifth left intercostal space in the midclavicular line — the mitral area. That’s where the first heart sound lands loudest That's the part that actually makes a difference..
Where is S2 heard best? At the base, specifically the second intercostal spaces right and left of the sternum (aortic and pulmonary areas). S2 is clearest there.
Can you hear S1 at the base? Yeah, but it’s quieter. The base favors S2. You’ll still pick up S1, just don’t use it as your reference there.
How do I know which sound is which? Feel the carotid pulse. The sound right at the pulse is S1. Or listen at the apex where S1 dominates, then move to base where S2 dominates.
Why does S2 split on inspiration? Because on
inspiration, intrathoracic pressure drops and venous return to the right heart increases. So that delays pulmonary valve closure just enough to separate the aortic and pulmonary components of S2 — you’ll hear it as a faint “dub… dub” instead of a single “dub” at the pulmonary area. It’s a normal finding, not a pathology, so don’t flag it as such Most people skip this — try not to..
What if I just can’t tell them apart? Slow down. Go back to the carotid trick, listen at the apex for a full minute, then the base for a full minute. Most people who say “I can’t hear it” are actually rushing between spots and missing the rhythm. The sounds don’t hide — your ear just needs repetition.
Bottom line: S1 lives at the apex, S2 lives at the base. The split sounds, the soft sounds, the shifted sounds — none of it matters until you’ve reliably placed S1 and S2 in their proper homes. Worth adding: palpate first, anchor with the carotid pulse, use light bell pressure, and don’t trust a chest you haven’t mapped by hand. Get that down and everything else in cardiac auscultation starts to make sense Most people skip this — try not to..
