Step By Step Heart Pump

The heart has four different sections, also known as chambers. You have the right and left atriums, and the right and left ventricles.

The right side of the heart (right atrium and right ventricle) is separated from the left side of the heart (left atrium and left ventricle).

The cause of this separation is from blood flow (oxygenated and deoxygenated). This separation is called the interventricular septum. 
From start to finish, I will describe how blood flow is pushed through the heart. 

Step 1: The first action is blood is received through the vena cava (superior and inferior) into the right atrium.

Step 2: The deoxygenated blood advances into the right ventricle. 

Step 3: The deoxygenated blood is then pushed through the pulmonary system into the lungs. 

Step 4: The blood, therefore, becomes oxygenated at this time.

Step 5: Oxygenated blood travels back through the pulmonary veins. 

Step 6: The oxygenated blood is pushed to the left atrium.

Step 7: It is then delivered to the left ventricle.

Step 8: The final step is oxygenated blood is pushed through the Aorta into the rest of the body. 

The Aorta is the biggest artery in the human body. This is a continuous unending cycle.

Therefore, the heart has a two-step pumping action:

The relaxation phase is known as the diastolic pressure, which receives deoxygenated blood from the vena cava (Steps 1-3).

The contraction phase is known as the systolic pressure, which pushes oxygenated blood flow away from the heart through the Aorta (Steps 5-8).

Arteries are large vessels that carry blood away from the heart.

Veins are blood vessels that bring blood back to the heart.

The best analogy for how arteries and veins function is similar to water passing through a hose or tube. When water is passed through a hose or tube, image the water as your blood, and the outside surface as your arteries and veins.