Is it normal for the first heart sound (S1) to be louder than the second heart sound (S2)?

Heart Sound Intensity: S1 vs S2

No, it is not normal for S1 to be greater than S2 in most auscultation locations. In normal cardiac auscultation, S2 is typically louder than S1 at the base of the heart (aortic and pulmonic areas), while S1 may be louder than S2 at the apex (mitral area).

Normal Heart Sound Intensity Patterns

• Base of the heart: S2 > S1 (normal finding)
• Apex of the heart: S1 > S2 (normal finding)

This pattern occurs because:

• S1 originates from mitral and tricuspid valve closure, making it more prominent at the apex
• S2 originates from aortic and pulmonic valve closure, making it more prominent at the base

Abnormal S1 > S2 Patterns

When S1 becomes abnormally loud compared to S2 in locations where this is not expected, it may indicate:

1. Mitral valve abnormalities:

   • Mitral stenosis (especially with pliable valves)
   • Short PR interval (allowing valve closure with greater force)

2. Conditions with high cardiac output:

   • Anemia
   • Thyrotoxicosis
   • Pregnancy
   • Arteriovenous fistula 1

3. Thin chest wall allowing increased transmission of sound 2

Abnormal S2 > S1 Patterns

When S2 becomes abnormally loud compared to S1, it may indicate:

1. Systemic hypertension (loud A2 component)
2. Pulmonary hypertension (loud P2 component)
3. Aortic dilation (loud A2) 2

Clinical Assessment

When evaluating heart sounds:

• Location matters: Always note where you're auscultating when comparing S1 and S2 intensity
• Dynamic changes: Use maneuvers to help distinguish heart sounds:
  • Respiration: Right-sided sounds (including tricuspid component of S1) increase with inspiration
  • Valsalva: Most murmurs decrease in length and intensity 1

Pathological Considerations

• Severe aortic stenosis: Often associated with a soft or absent A2, which can make S1 appear relatively louder 2
• Pulmonary stenosis: Characterized by wide splitting of S2 with a delayed P2 component 2
• Hypertension: May increase S2 intensity, particularly the A2 component 2, 3

Important Caveats

• A single S2 (due to inaudible A2) suggests severe aortic stenosis 2
• The absence of abnormal S2 findings makes severe aortic stenosis unlikely 2
• In pulmonary arterial hypertension, there is often increased S2 complexity and increased S2/S1 intensity ratio 3

Remember that proper auscultation technique and awareness of the location being examined are crucial for accurate interpretation of heart sound intensity relationships.