Video narration
How does blood move through your whole body without flowing backward? Think of the heart as a water pump driving fluid through a closed loop of pipes. It isn't one pump sending blood everywhere at once. It's one organ with two linked pumps, with the lungs between them. Follow one drop. After body tissues use oxygen, it returns oxygen-poor to the heart's right side. That side contracts, creating pressure, and sends it to the lungs, where carbon dioxide leaves and oxygen enters. Now the route flips. Oxygen-rich blood returns to the left side, which contracts and pushes it through the body. Tissues use the oxygen, and the drop starts back. Chambers contract and relax. Valves are one-way gates, stopping backward flow. So how does the pump keep the whole loop moving? Two linked pumps keep it moving: right side to lungs, left side to body, while valves keep the circuit flowing forward.