The heart is the body's hardest-working muscle. Whether you're awake or asleep, or exercising or resting, your heart is always at work. It pumps blood through arteries to deliver oxygen to organs and ...

Your heart is a muscular organ that helps circulate your blood, which delivers oxygen and nutrients to your tissues. There are four chambers and four valves in your heart, and each ensures proper ...

A night-shift worker finishes at dawn. Their phone says Tuesday, but their body feels like it's Monday. The body's internal ...