One-way doors
Inside your heart are four small doors called valves. Each one is made of thin, strong flaps.
When blood pushes forward, the flaps swing open. When blood tries to go backward, it pushes the flaps shut, like a door that only opens one way.
This keeps blood moving in one direction: in through the top rooms, down to the bottom rooms, and out of the heart.
Meet the four doors
The tricuspid valve (try-KUS-pid) is between the two right rooms. Tri means three, and it has three flaps.
The pulmonary valve (PULL-muh-nair-ee) is the door from the right ventricle out to the lungs.
The mitral valve (MY-trul) is between the two left rooms. It has two flaps. Long ago, a doctor thought it looked like a bishop's tall, pointed hat, called a miter, and the name stuck.
The aortic valve (ay-OR-tik) is the door from the left ventricle out to the aorta, the big tube that carries blood to your body.
Lub-dub: the sound of doors closing
When a doctor listens to your heart, they hear two sounds: lub-dub, lub-dub. That is not the sound of the muscle squeezing. It is the sound of the doors closing!
Lub is the tricuspid and mitral valves shutting as the bottom rooms start to squeeze. Dub is the pulmonary and aortic valves shutting when the squeeze is done.
Lub is a little longer and lower. Dub is shorter and sharper. See if you can hear the difference.
Listen in
Doctors listen to hearts with a stethoscope (STETH-uh-skope). It has a flat, round end that rests on your chest and two tubes that go in the doctor's ears. It does not hurt at all, though it can feel a little cold.
The first one was made about 200 years ago by a French doctor. He rolled a sheet of paper into a tube and found he could hear a heartbeat much better through it.
Try it: you can make a listening tube too. You need a paper towel tube and a friend or grown-up. Put one end gently on the left side of their chest, and put your ear to the other end. Make the room quiet.
Listen for lub-dub, lub-dub. Then have them jump 20 times and listen again. Is it faster now?