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Learn about the Heart

Posted on 5th Dec 2010 | In The Human Body


The heart is a muscular organ that supplies blood and oxygen to all parts of the body.

It is the center of the circulatory system. It is about the size of a clenched fist, weighs about 10.5 ounces and is shaped like a cone.

On average, your body has about 5 liters of blood continually traveling through it by way of the circulatory system. The heart, the lungs, and the blood vessels work together to form the circle part of the circulatory system. The pumping of the heart forces the blood on its journey and is central to the whole system.

What are the parts of the heart?

The heart is divided into four separate rooms or chambers that are separated down the middle by a muscular wall called the septum.

The four chambers are:

  1. The right atrium
  2. The left atrium
  3. The right ventricle
  4. The left ventricle

The two atriums are located at the top of the heart and are known as the holding chambers. The two ventricles are located at the bottom of the heart and are known as the pumping chambers. The upper chambers receive Oxygen-depleted blood coming back from the body and the lower chambers (ventricles) pump oxygen-rich blood back out to the body.

How does the heart work?

The left side of the heart is used to pump oxygen-rich blood out to the body. The oxygen, which is taken from the lungs, comes from the air we breathe in. Oxygen-rich blood is brought to the left atrium. The valve between the left atrium and the left ventricle opens to let the blood flow down into the ventricle.

After the left ventricle is filled, the valve between the left atrium and the left ventricle closes. This prevents backwash of the blood. The left ventricle then produces a mighty contraction – the “lub” sound – to push the blood out of the heart. Immediately, the valve from the left ventricle out to the aorta – the big blood vessel which carries blood to the tissues – opens and the blood actually begins its journey. The last valve of the heart then shuts again – the dub sound – to prevent flow of blood back into the heart.

When the blood comes back to the heart, it no longer has any oxygen in it. This oxygen-depleted blood enters the right ventricle, gets pushed through the valve leading to the right atrium and is, then, pumped into the lungs where it will be restocked with oxygen. This will start the whole process over again.

Valves or doors allow make sure that blood only flows in one direction and ensure there is no backwash of blood.

Arteries carry blood away from the heart and veins carry blood towards the heart.

What is the Cardiac Cycle?

The cardiac cycle is one heart beat. The cardiac cycle is completed when the heart fills with blood and the blood is then pumped from the heart. The audible sounds that can be heard from the heart are made by the closing of the heart valves.

There are three stages;

Diastole: This is when the chambers of the heart are relaxed and filling with blood.

Atria systole: Then the upper chambers (atria) contract and push blood down into the lower chambers (ventricles).

Ventricular systole: the ventricles contract and pump blood out into the body via the arteries.

With each beat 2-3 ounces of blood is moved.

The total cycle takes about 0.8 second which is the length of one heartbeat! This cycle or one heart beat happens 75 times per minute.

Interesting Facts

  • The device a doctor uses to listen to your heart is called a stethoscope.
  • The pulse is the measure of how many times your heart beats per minute.
  • The heart beats about 100,000 per day, 35 million times a year and over 2 and a half billion times in a life time! That’s a lot of heart beats!
  • A heart looks like a piece of red meat…or it should anyway! An unhealthy heart is yellow in color and covered in goo!
  • The female heart beats faster than the male heart.
  • At one time it was thought that the heart controlled a person’s emotions but of course now we know this is not true!

Want to learn more about the respiratory system? You can download a free heart worksheet and heart coloring page to practice what you’ve just learned.

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Elva O'Sullivan Ph.D is an educator and founder of She has created over 50 educational science products for the marketplace. To learn more about her and ScienceWithMe!® follow her on Facebook, LinkedIn and Twitter.

WOW! Elva O'Sullivan, founder of has one of the top 10% most viewed LinkedIn profiles for 2012. LinkedIn now has 200 million members. View Elva's profile!


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