Believe it or not, blood vessels contain blood. Don’t laugh. Some 3,000 years ago, people thought vessels carried air—and even urine.
For better or worse, everything we know today was built on ideas that came before us. There’s even a saying: “If we achieve greatness, it is because we stand on the shoulders of giants.” The “giants” of heart medicine are doctors and scientists who worked over the past 10,000 years. Some of their ideas were silly; many were just plain wrong. But their discoveries made modern medicine possible.

▲ Sumerians (about 5000 B.C.) believed the liver created blood. They wrote that the heart, not the brain, was the center of thought.
▲ Imhotep (about 2700–2670 B.C.) was an Egyptian pyramid engineer. He was also an astronomer, doctor, and more. He learned that blood circulates and the heart pumps it in pulses.

▲ Early doctors couldn’t just open a dead body and peek inside to study the heart. Dissecting humans was not allowed. Yet a Greek named Alcmaeon of Croton (about 500 B.C.) was the first known person to do it anyway. He figured out that the brain, not the heart, was where thinking happened. He noticed blood vessels came in two kinds: veins and arteries.

▲ Herophilus was a doctor in ancient Greece (about 300 B.C.). Many Greeks believed that air flowed through blood vessels. The word artery means “air carrier.” Herophilus taught most people that that was not right. Even so, some scholars hung on to the “air carrier” idea.

▲ Galen (about A.D. 130–199) was a doctor for Roman emperors. He wrote two books on medicine, which other doctors used for 1,400 years. Sadly, those books were full of errors. Here are just a few of them: Galen saw the heart as an oven for keeping blood warm. He thought blood flowed from one half of the heart to the other half through tiny holes. He also wrote that the body made blood directly out of the food you ate.
▲ Sick people have bad blood. Get rid of the bad blood. Then sick people will get well. Sound logical? Many doctors until the nineteenth century thought so. Bloodletting is draining a patient’s “bad blood.” Doctors cut open a vein or used leeches. Leeches are slimy creatures that attach to skin and suck out blood. Of course, these “treatments” just made people sicker—or dead.
Check It Out!
Put yourself in the shoes of an ancient doctor. Just by looking at the outside of your body, can you explain how things work? Here’s an example: Why does bruised skin go from black and blue to yellow and green and then to normal again?
A bruise means that blood vessels just under the skin are broken. The blood is red, but it doesn’t stay that way long. It loses its oxygen. Then it turns dark purple (or “black and blue”). Little by little, the body breaks down the loose blood. It gets rid of hemoglobin (red coloring matter), which makes the bruise turn from purple to yellow or green. When all of the blood has been broken down, the bruise disappears.
▲ Leonardo da Vinci (1452–1519 was a scientist, artist, and inventor. He drew the first accurate diagrams of the heart. He took apart dead bodies to do it.

▲ Andreas Vesalius (1514–1564) learned all kinds of wrong ideas about organs. He started out studying wrong diagrams like this one. Later, he corrected them and most of Galen’s wrong ideas. He published a new, better book on anatomy.
▲ William Harvey (1578–1657) figured out how the circulatory system really works. First off, blood does not come from food. Arteries pass blood to the veins in the outer parts of the body. Veins carry blood toward the heart. In other words, the circulatory system is circular. Harvey’s discoveries brought medicine out of the Dark Ages. In fact, all medicine took a huge leap forward with his findings—not just heart medicine. He lit the way toward modern heart science.
Try This!
Next time you’re having chicken or turkey for dinner, ask an adult to help you dissect, or cut up, the bird’s heart (if it’s included). Rinse the heart and set it on a plate. Look for yellow globs. That’s fat. Does the muscle feel tough or soft? How many tubes go in and out of the heart? Compare the heart to the liver. The heart has mechanical, or moving, parts. Slice it in half to see the chambers, tubes, and valves. Rinse the liver and slice it in half. It looks the same all over. When you’re done, throw out the organs. Then make sure to wash your hands with soap and hot water.