How does the heart work?

Your heart is two pumps in one, beating about 100,000 times a day without a single instruction from you. The heart has four chambers. The right atrium and ventricle send oxygen-poor blood to the lungs; the left atrium and ventricle send oxygen-rich blood to the whole body.

Read how it works: How does the heart work? · The history of understanding the heart · More boxes on Glassbox

Chapters in this interactive model

1. Inside the human heart: Two pumps side by side, four rooms, four one-way doors.
2. One heartbeat, step by step: Fill, squeeze, push, relax: the cardiac cycle and its lub-dub.
3. The heart’s own electricity: A built-in pacemaker, a deliberate delay, and a wave you can see on an ECG.
4. Two circuits, one heart: To the lungs and back, to the body and back: a figure of eight.
5. Blood pressure: 120 over 80: What the two numbers mean, how a cuff finds them, and why stretchy arteries matter.
6. Keeping it healthy, and what goes wrong: Narrowed arteries, heart attacks, CPR, and the habits that protect you.