What keeps blood from flowing back into a chamber of the heart

The pruesser and the amount of blood getting pushed from the heart makes sure that it doesnt flow back unless it does a full rotation around your body. Like a filter of a fish tank, the water cant go beck because of all that pressur pushing foward, later once that water has gon around the tank, it can go back and do it agian. 

p.s. can i get a crown? im almost to my next level and i would be happy!

The mitral valve does this between the left atrium and ventricle. The "lub" is the sound of the tricuspid and mitral valves closing. Each of your heart's ventricles has an outlet valve. The right ventricle uses the pulmonary valve to help move blood into the pulmonary arteries.