There's no safe way to get a close-up view of the human heart as it goes about its work: you can't just pop it out, take a look, then slot it back in.

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 ...

Researchers say they've found a system in the human heart that allows the organ to restart itself. Their discovery could lead to the replacement of pacemakers.

Here's a quick rundown of the systems of the human body, its vital organs and its "vestigial" organs, as well as a few fascinating facts about how the body works.

This article was originally published with the title “Work Performed by the Human Heart Estimated in Horse Powers” in Scientific American Magazine Vol. 21 No. 23 (December 1869), p. 361 doi:10 ...