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

Explanation

## Physiological Basis of Heart Sounds ### S1 (First Heart Sound) **Key Point:** S1 is produced by the closure of the atrioventricular valves (mitral and tricuspid) and marks the onset of ventricular systole. This is the correct statement in option 1. ### S2 (Second Heart Sound) **Key Point:** S2 is produced by closure of the semilunar valves (aortic and pulmonary). At the apex, it appears as a single sound; at the left sternal border, it physiologically splits into A2 (aortic closure) and P2 (pulmonary closure) during inspiration due to increased venous return to the right heart, delaying pulmonary valve closure. This is correct in option 2. ### S3 (Third Heart Sound) **High-Yield:** S3 occurs in early diastole (0.12–0.18 s after S2) due to rapid ventricular filling. **The critical error in option 3 is the claim that S3 is always pathological in adults.** S3 is physiological in children and young adults (< 30 years) due to rapid ventricular compliance. In older adults, S3 may indicate ventricular dysfunction, but it is NOT always pathological—it can occur in high-output states (anemia, pregnancy, thyrotoxicosis) and is a normal variant in some individuals. This is the **incorrect statement**. ### S4 (Fourth Heart Sound) **Key Point:** S4 occurs in late diastole (immediately before S1) due to atrial contraction and forceful atrial emptying into a stiff ventricle. It is heard best at the apex with the patient in the left lateral decubitus position. This is correct in option 4. ### Summary Table | Sound | Timing | Cause | Clinical Significance | | --- | --- | --- | --- | | S1 | Onset of systole | AV valve closure (M > T) | Normal | | S2 | End of systole | Semilunar valve closure (A > P) | Normal; splits in inspiration | | S3 | Early diastole (0.12–0.18 s after S2) | Rapid ventricular filling | Physiologic in youth; pathologic in age > 40 | | S4 | Late diastole (before S1) | Atrial contraction | Indicates decreased ventricular compliance | **Clinical Pearl:** The presence of S3 in an older adult (> 40 years) with systolic dysfunction is highly suggestive of heart failure and carries prognostic significance. However, S3 is NOT universally pathological—context matters.