True statement about the hea sounds:

Frequencies: S1 = 25-45 Hz; S2 = 50 Hz Durations: S1 = 0.1-0.17 sec; S2 = 0.1-0.14 sec. Durations of other hea sounds: Duration of S3- about 0.04 sec Duration of S4 - about 0.05-0.08 sec. The first hea sound is a low, slightly prolonged "lub", caused by vibrations set up by the sudden closure of the AV valves at the sta of ventricular systole. The second hea sound is a shoer, high-pitched "dup", caused by vibrations associated with closure of the aoic and pulmonary valves just after the end of ventricular systole. A soft, low-pitched third sound is heard about one-third of the way through diastole in many normal young individuals. It coincides with the period of rapid ventricular filling and is probably due to vibrations set up by the inrush of blood. A fouh sound can sometimes be heard immediately before the first sound when atrial pressure is high or the ventricle is stiff in conditions such as ventricular hyperophy. It is due to ventricular filling and is rarely heard in normal adults.