the heart as a pump

At its core, the heart is a pump — and more exactly a double pump, two pumps fused side by side into one organ. Like a pair of bellows working in lockstep, it draws fluid in on one side and pushes it out on the other, beat after beat.

The right side of the heart receives oxygen-poor blood returning from the body and pumps it the short distance to the lungs to pick up oxygen. The left side receives the freshly oxygenated blood from the lungs and pumps it, much more forcefully, out to the entire body. Because the left side has to drive blood through the whole system, its muscular wall is markedly thicker and stronger than the right.

Thinking of the heart as a pump is powerful because it lets us apply simple engineering ideas: how much fluid moves per beat, the pressure it generates, how filling and resistance change output. But the analogy has limits — unlike a mechanical pump, the heart adjusts its own rate and strength continuously and runs unattended for a lifetime.