But the R is known as our right side up, or the upward deflection wave because it increases the voltage, it makes it more positive now, what exactly takes place within the QRS? So here we have the electrical signal that permeated through the entire walls of our right and left ventricle. And now what begins to happen as soon as we reach the maximum point of the R way, this voltage here contraction of these ventricles begins to take place. And as the ventricles begin to contract, there is an increase in hydrostatic pressure. And that forces these two valve, the tricuspid and the biconspid valve, to close. And when they shut close, that's exactly what causes that first sound that we hear when we listen to our heart via a stethoscope.