So let's begin at a certain portion of our cardiovascular system. Let's suppose we begin in the right atrium of the heart. So number one, so the deoxygenated blood returns to the right atrium of the heart. So remember, the atrium always accepts the blood into our heart. Now, the blue arrow basically designates the movement of deoxygenated blood. But the red arrow designates the movement of oxygenated blood blood that contains our red blood cells with the oxygen.