Regarding the physiological basis of heart sounds, all of the following statements are correct EXCEPT:

Question

Accepted Answer

D. S2 is a single sound in infants and young children because the aortic and pulmonary valves close simultaneously. ## Physiological Basis of Heart Sounds

### Why Option B is the EXCEPT (Incorrect Statement)

**High-Yield:** S2 is produced by the closure of the semilunar valves (aortic and pulmonary). In infants and young children, S2 is characteristically **split** — not a single sound — because the pulmonary valve closes slightly after the aortic valve. This physiological splitting is actually more prominent in children due to their relatively lower pulmonary vascular resistance and greater respiratory variation. The statement that "S2 is a single sound in infants and young children because the aortic and pulmonary valves close simultaneously" is **incorrect**.

### S1 (First Heart Sound)
**Key Point:** S1 is produced by the closure of the atrioventricular valves (mitral and tricuspid) at the onset of isovolumetric contraction (ventricular systole). This is a correct statement. *(Guyton & Hall, Medical Physiology)*

### S2 (Second Heart Sound) — THE INCORRECT STATEMENT
**Key Point:** S2 is normally split, especially during inspiration, because inspiration increases venous return to the right heart, prolonging right ventricular ejection and delaying pulmonary valve closure relative to aortic valve closure. In infants and young children, this splitting is physiologically present and audible — the valves do **not** close simultaneously. A single S2 would actually suggest pathology (e.g., pulmonary hypertension causing early pulmonary valve closure). *(Harrison's Principles of Internal Medicine)*

### S3 (Ventricular Gallop)
**Clinical Pearl:** S3 occurs during the rapid filling phase of early diastole (0.12–0.16 s after S2) due to sudden deceleration of blood entering the ventricle. It is a **normal finding in children and young adults (< 40 years)** and becomes pathological in older adults, indicating ventricular dysfunction or heart failure. The statement that it is "always pathological in adults" is an overstatement but is less incorrect than Option B's outright factual error.

### S4 (Atrial Gallop)
**Key Point:** S4 occurs in late diastole, just before S1, when forceful atrial contraction pushes blood into a stiff, non-compliant ventricle. It is always abnormal and is seen in LVH, hypertension, and aortic stenosis.

| Heart Sound | Timing | Cause | Normal in Adults? |
|---|---|---|---|
| S1 | Start of systole | AV valve closure | Yes |
| S2 | End of systole | Semilunar valve closure (split) | Yes (split is normal) |
| S3 | Early diastole | Ventricular wall deceleration | Only if age < 40 |
| S4 | Late diastole | Stiff ventricle + atrial contraction | No (always abnormal) |

**Warning:** The key trap here is Option B — S2 is physiologically **split** in children, not a single sound. Simultaneous closure of aortic and pulmonary valves is not the normal physiological state at any age.

Answer

A. S1 is produced by the closure of atrioventricular valves (mitral and tricuspid) at the onset of ventricular systole

Answer

B. S3 (ventricular gallop) occurs during the rapid filling phase of early diastole and is always pathological in adults

Answer

C. S4 (atrial gallop) is produced by forceful atrial contraction against a stiff ventricle and occurs just before S1

Regarding the physiological basis of heart sounds, all of the following statements are correct EXCEPT:

Explanation

Physiological Basis of Heart Sounds

Why Option B is the EXCEPT (Incorrect Statement)

S1 (First Heart Sound)

S2 (Second Heart Sound) — THE INCORRECT STATEMENT

S3 (Ventricular Gallop)

S4 (Atrial Gallop)

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Heart Sound	Timing	Cause	Normal in Adults?
S1	Start of systole	AV valve closure	Yes
S2	End of systole	Semilunar valve closure (split)	Yes (split is normal)
S3	Early diastole	Ventricular wall deceleration	Only if age < 40
S4	Late diastole	Stiff ventricle + atrial contraction	No (always abnormal)