So this is when the cells of the ventricle repolarized. During this stage, these ventricles essentially empty out all that blood into our blood vessels. And because the hydrostatic pressure now decreases within our ventricles, these two semi lunar valves close. And when they shut close, that is the second sound that we normally hear in our lub dub. So lub is when our bicuspid and tricuspid valves close, but the dub takes place when our two semi lunar valves close. We have the pulmonary and the aortic semi lunar valve.