S3 and S4 are described as what kind of sound?

• A. Normal heart sounds
• B. A type of murmur
• C. An abnormal heart sound
• D. Closure of AV valves

Answer: (C)

S3 and S4 are extra heart sounds that occur outside the normal beat sounds (S1 and S2). They reflect changes in how the ventricle fills or how compliant the ventricle is, rather than normal valve closure or turbulent flow.

S3 happens early in diastole, right after S2, during rapid passive ventricular filling. In young people it can be normal, but in adults it commonly signals volume overload or heart failure, making it an abnormal finding. S4 occurs late in diastole, just before S1, when the atrium contracts against a stiff, noncompliant ventricle; this is typically associated with conditions like long-standing hypertension or left ventricular hypertrophy and is usually considered abnormal.

Because these sounds are not the normal heart sounds produced by AV valve closure (S1) or semilunar valve closure (S2), nor are they murmurs caused by turbulent flow, the best description is that they are abnormal heart sounds.