Why is the human heart called a double pump?

Hint: The heart is a muscular organ the size of a fist that is located just behind and slightly to the left of the breastbone. The heart circulates blood through the cardiovascular system, which is a network of arteries and veins.

Complete answer:
The human circulatory system is made up of three major parts: blood vessels, blood, and the heart. Because blood passes through the heart twice per circuit, it is referred to as a double circulatory system.
The right pump transports deoxygenated blood to the lungs, where it is oxygenated before returning to the heart.
The left pump circulates the newly oxygenated blood throughout the body. By the time this blood reaches the heart, it has become deoxygenated.
Blood enters the heart: The body's deoxygenated blood enters the right atrium of the heart.
Blood is pumped to the lungs: The right ventricle pumps this deoxygenated blood out of the heart and towards the lungs.
The lungs provide oxygen to the blood: Deoxygenated blood exchanges carbon dioxide for oxygen in the lungs. This is how it is oxygenated (contains oxygen).
Blood flows back to the heart: The oxygenated blood returns to the heart's left atrium.
The circulation of blood throughout the body: The left ventricle pumps oxygenated blood out of the heart and into the body.
Blood flows back to the heart: In exchange for carbon dioxide, oxygenated blood transports oxygen to body cells. The blood is deoxygenated before returning to the heart.
Thus, the human heart is called a double pump.

Note:
Your heart is located in the center of your chest, between your right and left lungs. It is, however, slightly tilted to the left. Although having a "big heart" is regarded as an admirable trait, it is unhealthy.