Which statement best differentiates S3 from S4?

Which statement best differentiates S3 from S4?

• A. S3 is due to rapid ventricular filling; S4 due to atrial contraction hitting a stiff ventricle
• B. S3 occurs during atrial contraction
• C. S4 occurs during systole
• D. S3 and S4 are both diagnostic of mitral stenosis

Answer: (A)

The main distinction lies in timing and mechanism of the fills and contractions in diastole. S3 happens early in diastole right after S2 when the ventricle rapidly fills; the sudden rush of blood and its deceleration create a low-pitched sound—the ventricular gallop. It reflects rapid ventricular filling and can be normal in younger individuals but often signals elevated filling pressures in older adults. S4, by contrast, occurs late in diastole, just before S1, when the atrium contracts to push blood into a stiff, noncompliant ventricle. The atrial kick against a rigid ventricle produces this sound, indicating decreased ventricular compliance. So the best differentiating concept is that S3 is due to rapid ventricular filling, while S4 is due to atrial contraction hitting a stiff ventricle. S3 is not during atrial contraction, S4 is not during systole, and neither sound is exclusively diagnostic of mitral stenosis.

The main distinction lies in timing and mechanism of the fills and contractions in diastole. S3 happens early in diastole right after S2 when the ventricle rapidly fills; the sudden rush of blood and its deceleration create a low-pitched sound—the ventricular gallop. It reflects rapid ventricular filling and can be normal in younger individuals but often signals elevated filling pressures in older adults.

S4, by contrast, occurs late in diastole, just before S1, when the atrium contracts to push blood into a stiff, noncompliant ventricle. The atrial kick against a rigid ventricle produces this sound, indicating decreased ventricular compliance.

So the best differentiating concept is that S3 is due to rapid ventricular filling, while S4 is due to atrial contraction hitting a stiff ventricle. S3 is not during atrial contraction, S4 is not during systole, and neither sound is exclusively diagnostic of mitral stenosis.