心室收缩
service contract───[劳经]劳务合同
gratuitous contract───无偿合同
service contracts───[劳经]劳务合同
voidable contract───可以撤销的合同
fixed-price contract───固定价格合同，定价合同
gratuitous contracts───无偿合同
general contractor───[经]总承包人；建筑公司
no-cut contract───无削减合同
rescind a contract───撤销合同
When the heart beats, an electrical signal passes from the top of the heart, near the atria (upper chambers), down through the ventricles (lower chambers), and the chambers contract in that order.───当心脏跳动时，一个电子信号就会从心脏的顶部传到一个心腔（位于上部），然后是位于下部的心腔，当它收缩时，也是按照这样的顺序。
So when the atria contract, the valves sandwiched between the atria and the ventricles open, and the blood in each atrium flows through its respective valve down into a ventricle.───所以当你的心房收缩时，夹在心房和心室之间的阀门就打开了，然后每个心房里的血液通过各自的阀门流向心室。
this time, the heart's electrical signal has passed from the atria into the ventricles, so while the atria relax, theventricles contract.───这个时候，心脏发出的电信号从心房传到心室，所以当心房放松时，心室就收缩。
Next, your heart'sventricles contract(an event called ventricular systole) and pump blood out of your heart.───接下来，心室收缩（称为“心室收缩期”）将血液泵出心脏。