What Is The Heart?

“Go to your bosom
Knock there and ask your heart
What it doth know”

William Shakespeare.


The heart is the symbol of life. It is also a symbol of love. The heart also stands for courage – we talk about being lion-hearted. It also indicates joy and happiness – as in being a hearty soul.

In medical terms, the heart is the pump that supplies blood and provides energy to the rest of the body. We’ll take a quick look at how the heart is structured. This small, yet powerful, muscular pump has always fascinated me, and I hope some of this amazement will be transferred to you too!


To work, to play, to do anything at all, the human body needs energy. This energy is provided by blood, which runs within tubes (blood vessels) called arteries and veins. ARTERIES carry “pure” or “red” blood from the heart to the other organs, and VEINS bring back “impure” or “blue” blood to the heart to be purified.

Blood circulates within these tubes, going around and around. And as it does, the body draws fuel in the form of chemicals and oxygen from the blood, and turns it into energy for work. Simultaneously, the waste materials produced by the body are dumped into the blood to be carried away and destroyed in other areas.

To circulate in the blood vessels, blood needs to be pumped. The heart is the pump, which provides the force for blood to travel to every part of the body.

The human heart is a hollow organ, roughly the size of your clenched fist, shaped like an upside-down pear and weighs around 11 ounces (or 300 grams). It’s walls are made up of muscle, just like the muscle in your arms and legs.

But, when they work for a long time, other muscles get tired and need rest. The heart muscle is different because it does not get tired. You can imagine how fortunate that is, since if the heart tires and stops, then life itself would come to an end!

The heart’s structure makes it an efficient, never-ceasing pump. On an average, the heart contracts and relaxes about 70 to 80 times per minute without you ever having to think about it

The heart is made up of four chambers – you can think of them as four rooms of a house. The chambers on top are called ATRIA (sing. Atrium), of which there are two – RIGHT and LEFT. The lower chambers are the VENTRICLES, again of which there are a right and left.

To understand how blood courses through this four chambered heart, let us take an imaginary trip through the blood stream – in something like a tiny rowing boat within the blood vessels!

Let’s begin our trip from the veins.

These carry the “impure” blood (or “blue” blood), into which all the wastes of the body have been dumped. As we float down the veins, we first reach the upper heart chamber on the right side – the RIGHT ATRIUM. The atrium is a kind of store room. Here, we wait for a short time, until the atrium is filled with blood.

Then we cross the TRICUSPID VALVE into the right lower chamber – the RIGHT VENTRICLE. The ventricle, unlike the atrium, is a powerful pump. Suddenly, and forcefully, we are propelled across the PULMONARY VALVE into a narrow tunnel, called thePULMONARY ARTERY. This is a tube that carries the “impure” blood to the LUNGS from the right ventricle.

The lungs are like bellows or balloons in the chest. There are two lungs, one on each side. When you breathe, air enters the lungs, and your chest moves up and down, or in and out. Watch your own chest as you breathe, and you can see this happen!

When “impure, blue” blood enters the lung, it mixes with the air you breathe in. OXYGEN (a “life-giving” gas in the air you breathe) enters the blood and the “impurities” (mainly another gas called CARBON DIOXIDE) leave it.

The blood is now “pure” or “bright red” as it leaves the lungs.

Shall we continue our journey then?

As we leave the lungs, we return to the heart. But this time, it is to the LEFT upper chamber – the LEFT ATRIUM. After a short wait here, again, we are guided across the MITRAL VALVE and into the left lower chamber – the LEFT VENTRICLE.

The left ventricle is the strongest chamber of the heart. It is the part of the heart that will pump blood to the rest of the body. The pressure that is produced in the left ventricle is similar to that in a garden hose when the water is turned on full-blast.

So, when we are in the left ventricle, suddenly a powerful thrust drives us through the AORTIC VALVE into another tube (or artery). This artery is the AORTA – the largest and toughest artery in the whole body. From the aorta, “pure” blood, carrying oxygen and energy-giving nutrients, is distributed to all organs of the body.

Blood flows to the brain, and you can think, see, dream – and read this article!

It flows to the stomach and intestines, and you digest today’s meal. Blood flows to your hands and legs, and you can write and walk and run. Each and every part of the body gets energy from the blood to do its special kind of work.

So, let’s put it all in a nutshell.

“Impure” blood from veins reaches the right atrium of the heart, and then flows to the right ventricle. From here, it passes through the pulmonary artery to the lungs, where oxygen is taken up, and wastes removed. The “pure” blood reaches the left atrium, and then the left ventricle. From here, it is powerfully pumped into the aorta, and then directed to all parts of the body.

Now, then, I expect you’d want to know why blood flows only in one direction. Why doesn’t it flow backwards?

The answer: Because there are VALVES to keep blood flowing in the same direction. A valve is something like a door. But while you can go both in and out of a door, a valve will only let you in ! You can’t get back through the same valve.

There are four valves in the human heart, one at each junction of two chambers.

  • Between the right atrium and right ventricle, there is the TRICUSPID VALVE. It is called tricuspid because it has three leaves or `cusps’.
  • From the right ventricle, blood is kept flowing towards the lungs by the PULMONARY VALVE.
  • In between the left atrium and left ventricle there’s the MITRAL VALVE. Some imaginative anatomist saw that it looked like bishop’s `miter’, and named it so !
  • Finally, the junction of left ventricle and aorta is guarded by the AORTIC VALVE.

Both the aortic and pulmonary valves have `cusps’ or leaves that are half-moon shaped, and they are fancifully called the semi-lunar valves.


The heart itself needs energy to do its work – pumping blood.

If you recall what we just discussed, blood from the left ventricle enters the aorta. The very first branches from the aorta are small “feeder” arteries called CORONARY ARTERIES, which turn back to supply blood to the heart muscle, bringing vital nutrients and oxygen to the heart.

Using these nutrients, the heart muscle shortens (or contracts) and the heart becomes smaller. It’s something like squeezing a balloon filled with water. Blood from inside the chambers is then pumped out with some force.

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