And this dub is called the second heart sound, or S2.

这个“dub”声被称为第二心音，或S2。

The second heart sound " dub" , or S2, originates from the closing of the aortic and pulmonary valves, right after the ventricles have ejected the blood.

第二心音“dub”， 即S2，是心室射血之后由于主动脉瓣和肺动脉瓣关闭产生的。

The second heart sound, " dub" , is called S2, and the noise comes from the aortic and pulmonic valves snapping shut to prevent blood from flowing backwards after it leaves the ventricles, effectively ending systole.

第二心音“dub”，它被称为S2，声音来自主动脉瓣和肺动脉瓣关闭，以防止血液在离开心室后反流，有效地结束心脏收缩。