How do you determine if a second heart sound is loud or normal?

Determining if the Second Heart Sound is Loud or Normal

To determine if S2 is loud, compare its intensity to S1 at the same location and assess the location of maximal intensity—a loud P2 is best heard at the upper left sternal border while a loud A2 is best heard at the upper right sternal border. 1

Systematic Assessment Approach

Location-Based Evaluation

The key to identifying a loud S2 is systematic comparison across cardiac auscultation sites:

• Listen at the upper left sternal border (pulmonic area) where P2 is normally loudest, then compare to the upper right sternal border (aortic area) where A2 is normally loudest 1
• Compare S2 intensity to S1 at each location to establish whether S2 is abnormally prominent 2
• Use the "inching" technique, moving the stethoscope systematically from the aortic area to the apex while keeping S2 as a reference point to accurately time and compare heart sounds 2

Respiratory Variation Assessment

Dynamic auscultation provides critical diagnostic information:

• Evaluate splitting patterns during normal and deep breathing to assess for underlying pathology 1
• Right-sided murmurs and sounds generally increase with inspiration, while left-sided sounds are louder during expiration 3

Clinical Contexts for a Loud S2

Pulmonary Hypertension

When pulmonary hypertension is suspected based on a loud P2:

• Look for associated signs of right ventricular hypertrophy including a right ventricular parasternal lift 3, 1
• A palpable second sound at the upper left sternal border suggests elevated pulmonary artery pressure 3
• Be aware that while a loud P2 suggests pulmonary hypertension, studies show this finding has limited sensitivity (60%) and specificity (22-41%) for definitively diagnosing this condition 4

Anatomic Variants

• In congenitally corrected transposition of the great arteries (CCTGA), S2 is characteristically loud due to the anterior position of the aorta, which can be mistaken for pulmonary hypertension 3, 5
• Fixed splitting of S2 during both inspiration and expiration in the presence of a midsystolic murmur suggests atrial septal defect 3

Normal Physiologic States

During pregnancy, cardiovascular changes alter S2 characteristics:

• A louder than normal S1 with prominent splitting and physiologically split S2 (which may widen and appear fixed in later pregnancy) are normal findings due to 50% increased blood volume and increased cardiac output 1, 6
• These changes are expected and do not require further workup in asymptomatic pregnant patients 6

Critical Diagnostic Distinctions

When S2 is Soft or Absent

Paradoxically, understanding when S2 is diminished helps establish what is "normal":

• A soft or absent A2, or reversed splitting of S2, indicates severe aortic stenosis 3
• The disappearance of A2 is specific (though not sensitive) for severe aortic stenosis due to valve calcification preventing normal forceful closure 7
• A normally split S2 reliably excludes severe aortic stenosis 7

Physical Characteristics Affecting S2

• As heart size increases (larger body surface area, hypertension), the amplitude of higher frequency components of S2 decreases 8
• S2 has greater amplitude than S1 above 150 Hz, likely due to vibrations within the aorta and pulmonary artery 8

Common Pitfalls to Avoid

• Do not confuse a loud S2 with other extra sounds: Use the inching technique to confirm timing relative to S2 as your reference point 2
• Pressure with the stethoscope eliminates S4 but not ejection sounds or split S1, helping differentiate these from a loud S2 2
• In elderly patients with severe aortic stenosis, the typical soft A2 may be less apparent due to vascular changes with aging 3
• In CCTGA, the loud S2 from anterior aortic position can mimic pulmonary hypertension—consider this diagnosis especially with dextrocardia 3, 5