People once thought the heart was the seat of thought and emotion, but now we know better: it is simply a muscular pump that beats tirelessly to keep blood flowing. Unlike other muscles in the body, which need to rest and recover after heavy use, the heart is built to work nonstop. It beats 70 times a minute, 100,000 times a day, and 40 million times a year - pumping enough blood in the average lifetime to fill three supertankers.

With each beat it squeezes out about a cupful of blood, using sufficient force to keep blood moving through the body’s 60,000 miles (100,000 km) of blood vessels. A continual supply of fresh blood is vital to the body’s cells because without it, they will die of oxygen starvation in minutes.

Inside the Heart

The heart is divided into two halves, allowing it to work as two pumps in one. The right half pumps stale blood to the lungs to pick up oxygen from air. The left half pumps the oxygen-rich blood to the rest of the body.


One-way valves stop blood flowing backward.


The heart has two small top chambers called atria.

Left ventricle

This large, muscular chamber pumps blood to most parts of the body.

Right ventricle

The smaller right-hand chamber pumps blood to the lungs and back.

Heartbeat Cycle

Each beat of the heart involves several carefully timed steps. The whole sequence is controlled by a wave of electricity that sweeps through the heart’s muscular wall, triggering the contraction of muscle cells.

1. Filling up: Between heartbeats, blood enters the heart through veins and collects in the top chambers (atria).

2. Atria contract: The top chambers contract, pushing the blood through valves into the two lower chambers (ventricles).

3. Ventricles contract: Finally, the ventricles contract with great force, pushing the blood out to every part of the body.