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NAVLE® Question of the day

MO TU WED TH FR

November 28, 2024

NAVLE

One description of a typical heart sound is "lub-dub."

What makes the first heart sound (S1) (i.e., the "lub")?

A - Rapid atrial and auricular expansion due to cranial and caudal vena cavae contraction

B - Aortic and pulmonic valves shut and the mitral and tricuspid valves open

C - End of rapid ventricular filling period

D - Atrial contraction

E - Closure of atrioventricular valves, opening of semilunar valves

Touche! You chose E - Closure of atrioventricular valves, opening of semilunar valves

The first heart sound (S1 or the "lub" in "lub-dub") is caused by closure of the atrioventricular valves (AV valves, mitral and tricuspid) and opening of the pulmonic and aortic valves (semilunar valves). This is the end of diastole and start of systole.

The second sound (S2) is the closure of the aortic and pulmonic valves and opening of the AV valves. This is the end of systole and start of diastole.

A third sound (S3) is the end of rapid ventricular filling and a fourth sound (S4) is atrial systole (atrial contraction).

You can often hear all 4 sounds in horses, but typically hear only S1 and S2 in cattle and small animals.