Cardiac Auscultation Guide: S1 vs S2, Murmurs & Exam Technique
Systole vs Diastole: Understanding S1 and S2 Heart Sounds
At the core of cardiac function lies the rhythmic interplay between systole and diastole—a perpetual cycle forming the foundation of circulation. Systole represents contraction, where ventricular muscles generate the pressure to propel blood through the pulmonary and systemic circuits. This high-pressure event creates distinct acoustic signatures as the mitral and tricuspid valves slam shut, generating the first heart sound (S1).
Diastole follows as the heart’s moment of respite—a relaxation phase allowing chambers to refill while creating its own characteristic sounds as semilunar valves close, producing the second heart sound (S2). The precision-engineered diaphragm of your stethoscope captures these nuances with remarkable clarity, letting you distinguish phases by timing, intensity, and pitch. With practice, recognizing these normal patterns becomes second nature—your baseline for spotting pathology.
Phases of the Cardiac Cycle: Contraction, Relaxation, Filling & Ejection
The cardiac cycle is a masterpiece of biological timing. After atrial systole completes ventricular filling, ventricular contraction builds pressure until it exceeds that of the great vessels; semilunar valves open and ejection begins.
Next comes isovolumetric relaxation—a brief interval when all valves are closed—followed by ventricular filling through rapid passive flow and slower diastasis. Each phase produces distinct acoustic phenomena via valve closures, turbulence, or chamber-filling dynamics. With a well-maintained dual-lumen stethoscope, subtle timing shifts that hint at valvular disease, conduction issues, or altered compliance become audible—elevating auscultation from simple listening to functional analysis.
Wiggers Diagram Explained: ECG, Pressure, Volume & Heart Sounds
The Wiggers diagram acts as cardiology’s score, aligning ECG, chamber and vessel pressures, ventricular volume, heart sounds, and valve events in time.
Within this framework, S1 maps to AV-valve closure after the QRS complex; S2 aligns with semilunar-valve closure at the end of the T wave. Additional sounds like S3 (early diastolic filling) and S4 (atrial contraction) occupy predictable positions. High-fidelity acoustics help you correlate what you hear with underlying physiology.
Pathologic Heart Sounds & Murmurs: Systolic vs Diastolic Clues
Murmurs—the sustained sounds of turbulent flow—convey crucial information about valve function and structure. Timing (systolic vs diastolic), location, intensity, pitch, quality, and radiation each add diagnostic weight.
Systolic murmurs may reflect stenotic semilunar valves or regurgitant AV valves. Diastolic murmurs often indicate semilunar regurgitation or AV-valve stenosis. Extra sounds—an opening snap in mitral stenosis, a mid-systolic click in mitral valve prolapse, or a pericardial friction rub—tell specific stories. Chestpiece design matters: the bell’s low-frequency sensitivity is key for S3 gallops and mitral stenosis. Optimal pressure and precise placement often determine whether subtle findings are heard at all.
Cardiac Auscultation Technique: Stethoscope Placement, Bell vs Diaphragm, Positions
Five key listening posts:
• Aortic: 2nd right intercostal space
• Pulmonic: 2nd left intercostal space
• Erb’s point: 3rd left intercostal space
• Tricuspid: 4th left intercostal space
• Mitral: 5th left intercostal space at the midclavicular line
Pressure & piece selection:
• Firm pressure with the diaphragm emphasizes higher-frequency sounds (most murmurs and normal heart sounds).
• Light pressure with the bell reveals low-frequency phenomena (e.g., mitral stenosis, S3).
Patient positioning & breathing:
• Listen during quiet respiration and during held expiration.
• Reassess supine, left lateral decubitus, and leaning forward to optimize specific findings.
A systematic, repeatable protocol lets the instrument disappear—freeing you to focus on interpretation.
How to Get Better at Cardiac Auscultation: Practice & Pattern Recognition
Expertise grows with repetition and correlation. What begins as distinguishing S1 from S2 evolves into recognizing splits, physiologic variants, and pathology against the body’s complex acoustic background. Each encounter connects sounds to other clinical data, building a mental library for rapid recognition. With the right tools and deliberate practice, listening becomes understanding.
Looking for a clearer bedside sound? Explore our full range of stethoscopes designed for precise cardiac listening.
“Auscultation is not just a skill—it’s a mindset. The most meaningful sounds often lie just beneath the noise.”
