When the ventricle empties by its contraction the wall relaxes and the back flow from the artery is prevented by crescentic-shaped valves placed where the artery joins the ventricle.

A similar arrangement of valves is on the left side of the heart.

The pressure given the blood by the contraction of the right ventricle sends it through the lungs; from these, after it has been oxygenated, it passes into the left auricle, then into the left ventricle and from this into the great artery of the body, the aorta, which gives off branches supplying the capillaries of all parts of the body.

Both of the auricles and both of the ventricles contract at the same, time, the ventricular contraction following closely upon the contraction of the auricles.

Contraction or systole is followed by a pause or diastole during which the blood flows from the veins into the auricles.