Who's squeezing the toothpaste tube from the middle?

是谁从牙膏管的中间开始挤的？

And two, the ventricles need to squeeze like their squeezing a tube of toothpaste -- from the bottom up -- to accelerate the blood through the big arteries at the top of the heart.

第二，心室需要挤压，就像挤压一管牙膏一样——自下而上——来加速血液通过心脏顶部的大动脉。