The second heart sound (S2) is normally single during expiration but splits physiologically during inspiration due to the slightly different timing of aortic and pulmonary valve closure. S2 has two components, the aortic component (A2) followed by the pulmonary component (P2). Variations in S2 can occur including wide or fixed splitting, reversed splitting, or it can remain single. These variations provide clues to underlying cardiac conditions such as septal defects, valvular stenosis, or conduction abnormalities.

1. ‫الرحمن‬ ‫هللا‬ ‫بسم‬‫الرحیم‬

2. Second Heart Sound
MECHANISM AND VARIATIONS

3. S2
 The second heart sound (S2) is due to the closure of aortic and pulmonary valves. It has two
components:
 Aortic component (A2) due to aortic valve closure.
 Pulmonary component (P2) due to pulmonary valve closure.
 The aortic component (A2) is followed by the pulmonary component (P2).
 Normally, during expiration, both valves close almost simultaneously, and hence, second
heart sound is single. During inspiration, the aortic valve closes early due to increased
capacitance of pulmonary vascular bed while pulmonary wall closes late due to increase in
right ventricular volume. This results in a physiological inspiratory splitting of second heart
sound.
 Loudness of A2 or P2 is proportional to the respective pressures in aorta or pulmonary
artery at the onset of diastole.

4. Variations in the Intensity of Second
Heart Sound
Wide Mobile Split Reversed (paradoxical) Splitting
• Delayed electrical activation
of right ventricle
• Right bundle branch block
• Ectopic from left ventricle
• Prolonged right ventricular systole
• Pulmonary stenosis
• Pulmonary hypertension
• Massive pulmonary embolism
• Early aortic closure
• Mitral regurgitation
• Delayed electrical activation of left ventricle
• Left bundle branch block
• Ectopic from right ventricle
• Prolonged left ventricular systole
• Hypertension
• Severe aortic stenosis
• Hypertrophic cardiomyopathy
• Patent ductus arteriosus
• Severe left ventricular dysfunction
• Early pulmonary valve closure
• Tricuspid regurgitation
• Early electrical activation of right ventricle
• Wolff-Parkinson-White syndrome (type B)

5. Variations in the Intensity of Second
Heart Sound
Wide Fixed Splitting Single Second Heart Sound
• Atrial septal defect
• Severe pulmonary stenosis
• Severe right ventricular
failure
• Severe aortic stenosis
or markedly attenuated A2)
• Severe pulmonary stenosis
(absent or markedly
attenuated P2)
• Tetralogy of Fallot