Describe all types of heart sounds.

Heart Sounds: Complete Classification

Heart sounds are classified into four primary categories: S1 (first heart sound from atrioventricular valve closure), S2 (second heart sound from semilunar valve closure), S3 (early diastolic filling sound), and S4 (presystolic atrial contraction sound), along with additional sounds including ejection sounds, opening snaps, and clicks.

Primary Heart Sounds

First Heart Sound (S1)

• S1 occurs with closure of the mitral and tricuspid valves at the onset of ventricular systole 1, 2
• The first major component (M1) coincides with mitral valve closure, occurring approximately 0.06 seconds after the Q wave on ECG 1
• The second component (T1) relates to tricuspid valve closure, occurring approximately 0.09 seconds after the Q wave 1
• M1 and T1 result from sudden deceleration of blood following valve closure, creating vibrations in the cardiohemic system 1
• In mitral stenosis, the Q-M1 interval is delayed to 0.10 seconds, potentially causing reversed splitting of S1 1
• Mechanical heart valves produce S1 with higher frequency components and greater energy compared to native valves 3

Second Heart Sound (S2)

• S2 is generated by closure of the aortic (A2) and pulmonic (P2) valves at the end of ventricular systole 4
• Fixed splitting of S2 during both inspiration and expiration suggests atrial septal defect 4
• A soft or absent A2 component indicates severe aortic stenosis 4
• Reversed splitting of S2 (P2 before A2) denotes severe aortic stenosis or left bundle branch block 4
• Physiologic splitting (wider during inspiration) is normal, with P2 delayed due to increased right ventricular filling 4

Third Heart Sound (S3)

• S3 occurs in early diastole during rapid ventricular filling 4
• This low-pitched sound may be normal in children and young adults but suggests ventricular dysfunction or volume overload in older adults 4

Fourth Heart Sound (S4)

• S4 occurs in late diastole immediately before S1, coinciding with atrial contraction 4
• This presystolic sound requires sinus rhythm and indicates decreased ventricular compliance 4
• S4 is commonly heard in conditions causing ventricular hypertrophy or stiffness 4

Additional Cardiac Sounds

Ejection Sounds

• Aortic ejection sounds occur 0.13 seconds after the Q wave and coincide with full opening of the aortic valve 1
• An early aortic systolic ejection sound heard during both inspiration and expiration suggests a bicuspid aortic valve 4
• Pulmonic ejection sounds occur 0.10 seconds after the Q wave in pulmonic stenosis 1
• Ejection sounds heard only in the pulmonic area during expiration indicate pulmonic valve stenosis 4
• In patients without valvular stenosis, pulmonic ejection sounds may occur 0.18 seconds after the Q wave 1
• Ejection sounds result from sudden acceleration of blood as valves reach fully opened position 1

Opening Snaps

• Opening snaps occur in mitral or tricuspid stenosis during early diastole when stenotic valves open 4
• The opening snap is absent in isolated aortic regurgitation, helping distinguish the Austin-Flint murmur from mitral stenosis 4

Clicks

• Mid-to-late systolic clicks are characteristic of mitral valve prolapse 4
• These clicks occur when redundant mitral valve leaflets prolapse into the left atrium during systole 4

Clinical Significance and Diagnostic Approach

Key Auscultatory Findings

• Fixed splitting of S2 with a grade 2/6 midsystolic murmur at the pulmonic area strongly suggests atrial septal defect 4
• Soft or absent A2 with reversed S2 splitting indicates severe aortic stenosis requiring echocardiography 4
• The combination of ejection sound timing and respiratory variation helps differentiate aortic from pulmonic valve abnormalities 4, 1

Dynamic Auscultation

• Right-sided heart sounds (including T1 and pulmonic sounds) increase with inspiration due to increased venous return 4
• Left-sided sounds typically increase during expiration 4
• The Valsalva maneuver decreases most heart sounds except in hypertrophic cardiomyopathy and mitral valve prolapse 4

Common Pitfalls

• Do not confuse the second component of S1 with an ejection sound—the second S1 component may represent either tricuspid closure or aortic valve opening depending on timing 2, 5
• In 70% of patients, both mitral and tricuspid closure contribute to the first major component of S1, making isolated valve assessment challenging 5
• Mechanical valve sounds have distinctly different acoustic properties than native valves, with higher frequencies and energy that vary by valve position and recording location 3