Beyond Lub-Dub: Stethoscopes Tells the Whole Story
When Extra Heart Sounds Change Care
There’s a moment every clinician remembers—when you first hear something beyond the basic "lub-dub" and realize your stethoscope just became a window into a patient’s physiology. Those extra heart sounds that textbooks try to teach through mnemonics and diagrams suddenly become real, immediate, and clinically meaningful.
I’ve been thinking about this lately because of a case that reminded me why careful auscultation still matters. A 67-year-old woman comes in for routine follow-up, feeling "a bit more tired lately." Her vital signs looked fine. Her echo from six months ago was stable. But when I placed my stethoscope at her apex (pun intended?), I heard it—a clear third heart sound that wasn’t there at her last visit.
That sound changed everything. It told me her heart was struggling in ways that her other tests hadn’t yet captured. Within two hours, we had adjusted her medications and consulted cardiology. Sometimes the most important information isn’t in the lab results or imaging. It’s right in front of us, waiting for someone to listen carefully enough to hear it.
What Your Heart Is Really Saying: S1, S2, S3 & S4 Basics
The basic S1 and S2 sounds—that familiar "lub-dub"—are just the beginning of the conversation. Think of them as the baseline rhythm section in a song. S1 marks when the mitral and tricuspid valves snap shut at the start of each heartbeat. S2 is the aortic and pulmonic valves closing when the heart finishes squeezing.
But sometimes the heart has more to say. That’s where S3 and S4 come in—the extra sounds that transform routine auscultation into sophisticated cardiac assessment. These aren’t random noises. They’re specific acoustic signatures that tell you about volume status, ventricular compliance, and how well the heart is handling its workload.
The tricky part? These sounds are subtle. They hide in the spaces between the main beats, whispering information that you’ll miss if you’re not listening for them specifically. And timing—timing is everything.
S3 Gallop: The Sound of Volume Overload (Early Diastole)
S3 is the sound of a heart dealing with volume overload. Picture trying to fill a water balloon too quickly. There’s that moment when the balloon stretches suddenly to accommodate the rush of water. That’s essentially what’s happening when you hear an S3.
It occurs about a tenth of a second after S2, creating a "lub-dub-ta" rhythm that’s been compared to the cadence of "Tennessee." The heart fills rapidly during early diastole, and if the ventricle is dilated or struggling, you’ll hear that distinctive sound as blood rushes in.
Here’s what I’ve learned about finding S3 in practice: forget trying to hear it with the patient sitting up. Get them in a left lateral position, use the bell of your stethoscope at the cardiac apex, and apply the softest pressure. Light touch is important. If you press too hard, you’ll turn your bell into a diaphragm and lose the low-frequency sounds entirely.
In young adults an S3 might be normal, young hearts are vigorous and compliant. But in adults over 40, it’s almost always pathological. It’s the acoustic signature of heart failure, telling you the ventricle is dilated and working harder than it should to handle its volume load.
S4 Gallop: The Sound of Stiff Ventricles (Atrial Kick)
S4 tells a different story entirely. If S3 is about too much volume, S4 is about too much resistance. It’s the sound of an atrium working overtime to push blood into a stiff, non-compliant ventricle.
The timing is crucial here—S4 comes just before S1, creating a "ta-lub-dub" pattern that people often recite "Kentucky." It happens during atrial contraction, when the atrium gives that final squeeze to top off ventricular filling. If you’re watching an ECG simultaneously, S4 coincides with the P wave.
Unlike S3, S4 is always abnormal in adults. It’s the sound of a ventricle that’s lost its flexibility. It comes from long-standing hypertension, aortic stenosis, or ischemic heart disease. The left atrium is essentially saying, "I’m working as hard as I can to fill this stubborn ventricle."
Finding S4 requires the same technique as S3. Left lateral position, bell at the apex, light pressure. But you’re listening for that extra sound just before the main "lub," not after the "dub."
Stethoscope Quality & Technique: Bell, Pressure & Positioning
The quality of your stethoscope matters more for extra heart sounds than almost any other aspect of physical examination. These are subtle, low-frequency sounds that cheaper instruments simply can’t transmit clearly. You need a stethoscope engineered specifically for acoustic clarity, with tubing designed to minimize sound loss and a bell that can pick up those low-pitched vibrations.
I’ve noticed that when I switched to my Apex stethoscope, S3 and S4 sounds became clearer and more confident in my assessments. The difference isn’t just academic—it’s clinically meaningful. When you can trust what you’re hearing, you make better decisions about medication adjustments, fluid management, and when to dig deeper with additional testing.
Clinical Context Matters: Interpreting S3/S4 by Patient Profile
The real skill isn’t just hearing these sounds—it’s interpreting them in context. An S3 in a 25-year-old athlete probably doesn’t worry me. The same sound in a 65-year-old with diabetes and hypertension changes my entire approach to their care.
S4 often appears before patients develop obvious symptoms. You might hear it in someone with well-controlled hypertension who feels fine but whose ventricle is starting to stiffen. It’s an early warning system, telling you to optimize their blood pressure control before they develop more obvious signs of diastolic dysfunction.
When the Heart Speaks, Listen: Acting on S3/S4 at the Bedside
That patient I mentioned earlier? Her new S3 was the first sign that her heart failure was progressing despite stable symptoms. We caught it early enough to adjust her medications and prevent a hospitalization. Three months later, the S3 was gone, and she was feeling better than she had in months.
This is why careful auscultation still matters in an age of sophisticated imaging and biomarkers. Your stethoscope can pick up changes in real-time, at the bedside, without waiting for lab results or scheduling studies. It’s immediate, intimate, and surprisingly sensitive when you know what to listen for.
Listen Beyond Lub-Dub: The Takeaway for Everyday Practice
The heart has been trying to tell us stories for as long as we’ve been listening. S3 and S4 are just part of its vocabulary—subtle but important words in the conversation between clinician and patient. The question is whether we’re skilled enough to hear what it’s saying.
Next time you place your stethoscope on a patient’s chest, take a moment to really listen. Beyond the basic lub-dub, what else is the heart trying to tell you? Sometimes the most important information isn’t the loudest—it’s the extra sound hiding between the beats, waiting for someone with the right tools and training to hear its message.
