 First, let's get oriented to the schematic. We will be drawing an anterior superior view. This simply means you would be looking at a person face to face. To get started, the heart is nothing but a simple box divided into four equal components. Draw a box, then divide the box into four equal compartments. Second, in the left hand corner of the page, place the word right. And on the right hand side of the page, place the word left. This will be contralateral to your position and allows you to view the person's right and left side of the heart as if you were looking at them face to face. Now, look at the box that you have made. The top two compartments are called atriums, so you have a right atrium and a left atrium. The bottom two compartments are called ventricles, meaning you also have a right ventricle and a left ventricle. The heart's left atrium receives oxygenated blood that has passed through the lungs via the pulmonary veins. Oxygenated blood is then pushed through the left atrium into the left ventricle. Blood leaves the left ventricle via the aorta. The oxygenated blood is then delivered to the body tissues from metabolism. When the blood vessels reach the tissues, they release oxygen into the tissue and pick up carbon dioxide left over from previous metabolic processes. This is called internal respiration. Next, the deoxygenated blood with high levels of carbon dioxide travels back into the heart from the body tissue. The blood from the lower extremities enter into the inferior vena cava and blood from the upper extremities enters into the superior vena cava. Both of the structures are veins. The blood from the superior and inferior vena cava empties into the right atrium. Blood from the right atrium flows into the right ventricle and then flows into the pulmonary trunk. Once the blood enters the pulmonary trunk, it travels towards the lungs. Along the way, the pulmonary trunk branches into the left and right pulmonary arteries. As the pulmonary arteries reach the lungs, carbon dioxide is released from the arteries and oxygen enters the pulmonary veins. This process is called external respiration.