The heart is the body's hardest-working muscle. Whether you're awake or asleep, or exercising or resting, your heart is ...

Circulatory system: Blood vessels. Laid end-to-end, an adult's arteries, veins and capillaries would stretch for about 100,000 miles - enough to wrap around the world nearly four times.

Learn about the circulatory system with these interactive learning resources for KS2 Science students aged 7-11 from BBC Bitesize.