Your heart is a hollow organ about the size of your fist. Inside your heart there are actually four hollow sections called chambers that are surrounded by muscle. The top two chambers are called atria, while the bottom two chambers are called ventricles.

To help you remember what your heart does, it is divided into sides (right and left) to make two pumps. The pump on the right side is made up of the right atrium and right ventricle. When your heart muscle relaxes, the right atrium fills up with blood from all over your body and then lets it go down to the right ventricle. Then your heart muscle squeezes really fast and sends blood from the right ventricle to the lungs, so they can fill your blood with oxygen.

At the same time that this is happening, the pump on the left side of your heart does the opposite! The left atrium fills up with blood that has been filled up with oxygen from the lungs. It lets this blood go down to the left ventricle, then your heart squeezes really quickly and sends all of this blood to your body to feed your cells with oxygen. Pretty Cool!

But how does the blood know to go from one place to another?

Well, your heart is part of your circulatory system, which is made up by your heart, blood, arteries and veins. Arteries are tubes that go from the heart directly to your lungs, head, muscles, and to all of your other cells to give them oxygen, water, and nutrients. Then veins take the blood back to your heart so it can be pumped out to your body again and again!

An easy way to remember what arteries and veins do is to match the words that begin with "a's." Arteries take blood away from the heart (arteries = away), while veins bring blood back to the heart (no "a's").

Check out this picture to see more about the heart and how it works:

So, how does a heart attack happen?

STOP AND THINK