Circulatory System

The heart is a hollow, muscular organ that maintains blood circulation throughout the body. Learn how the circulatory system - your heart, blood vessels and blood - bring nutrients to the body.

James Harrison's blood contains a rare and powerful antibody that's saved millions of Australian babies. Now, at age 81, after donating 1,173 times, he's hoping someone else will pick up where he left off.

What makes your heart beat is not a simple as you think. Take a look into what makes this crucial organ tick with the help of the information inside this article.

Every second of the day, blood bustles through your body, bound for your brain, toes and everything in between. How does your heart receive its fair share of the good stuff?

When it comes to the heart, timing is critical. An irregular heartbeat is inefficient and deprives the body of blood. So what sets your ticker's rhythm?

Lub-dub, lub-dub, lub-dub, that's usually the sound of a happy heart. But what's responsible for that steady, comforting beat, and what if your heart doesn't sound like that?

The heart is crucial to life and the focus of love. Explore the parts of the heart and how your heart works, plus take a look at real pictures of human hearts with this gallery.

Creatinine is a chemical molecule that is present in the serum (liquid portion) of the blood. The amount of creatinine produced depends on a person's muscle mass. But how is it measured?

The natriuretic peptides are sometimes called the body's "natural diuretics" because they lower the concentration of sodium in the blood.

Why don't you have two hearts? Here's a hint: It's the same reason why you have one liver, but two eyes. Would a second heart help you live better?

The heart is one of the strongest muscles in the body. Learn about this extremely vital part of the body.

When you donate blood, your blood type is an important factor in how useful your donation may be. Just what are blood types?

The heart is a vital organ that basically serves as a pump. Learn about heart chambers and valves, blood flow, the heart's electrical system and blood supply. Read more about how this amazing organ works.