The heart pumps blood through circuit(s).

The heart pumps blood through the pulmonary and systemic circuits of the circulatory system. 

In humans, the blood flows from the heart in two circuits or paths. The pulmonary circuit allows blood to flow between the heart and the lungs, while the systemic circuit allows blood to flow between the heart and the rest of the body.

The right side of the heart pumps deoxygenated blood to the lungs through the pulmonary circuit to oxygenate the blood. The oxygenated blood returns to the heart and is pumped by left side of the heart through the systemic circuit to oxygenate the rest of the body. Then, blood becomes deoxygenated as is passes through the body. The deoxygenated blood from the body flows back into the heart via the systemic circuit. The deoxygenated blood onces again moves through the pumonary circuit for oxygenation and the cycle begins again. 

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