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Healtheuniversity > English > Cardiac College > Treat Heart Disease > How The Heart Works > How the Heart Works

How the Heart Works

A heart showing the upper and lower chambers, valves, aorta, vena cava and the pulmonary arteries and veins. Arrows pointing the direction of the blood flow from the body to the heart, from the heart to the lungs, from the lungs back to the heart and from the heart out to the body.

The flow of blood through the heart. See how blood flows through your heart (opens in new window) »

Your heart is located slightly to the left of the centre of your chest. It is about the size of your fist.

Your heart is a muscle that pumps more than 100,000 times per day.

The heart’s job is to supply the entire body with oxygen-rich blood. To do this, the heart has:

The Heart’s Pump

The heart is made up of:

  • 4 chambers:
    • 2 upper chambers called the atria
    • 2 lower chambers called the ventricles
  • small valves that:
    • open and close when your heart beats
    • keep the blood flowing through the heart in one direction
    • link the upper and lower chambers of the heart

Blood is pumped through these chambers and valves in the following way.

  1. Blood returning to the heart from the body (by way of the vena cava) flows into the right atrium.
  2. When the atrium contracts, it forces blood through the tricuspid valve into the right ventricle.
  3. From the right ventricle, it is pumped through the pulmonary artery to the lungs where it picks up oxygen.
  4. From the lungs, it returns to the heart through the left atrium.
  5. From the left atrium, it goes through the mitral valve to the left ventricle.
  6. The left ventricle pumps the blood into the aorta and then to all parts of the body.

Each time the heart contracts or beats, this pumping action is felt in the large arteries of the body as a pulsing sensation and that is what you feel when you take your pulse.

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The Heart’s Electrical System

An ECG tracing showing a normal heart rhythm.
A normal electrocardiogram (ECG)

The heart sends electrical signals from one part of itself to another. These signals make each chamber of the heart contract in the correct sequence to squeeze blood from one area to the next, eventually pumping blood out of the heart to the rest of the body.

The signal is started in the right atrium by a group of special cells called the Sino-Atrial Node (SA-Node). The SA-Node is often called the pacemaker of the heart. It makes sure a signal is sent a certain number of times per minute.

The passage of the electrical signal through the heart can be recorded on an electrocardiogram. Learn more about electrocardiogram »

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The Heart’s Blood Supply

Image of a heart showing the coronary arteries and the aorta. Right coronary artery, left main branch, circumflex artery and left anterior descending artery.
Arteries of the heart

The heart’s job is to deliver blood filled with oxygen and nutrients to the entire body.

The heart also needs its own blood supply so that the muscle is able to contract (squeeze). The heart’s blood supply is delivered through the coronary arteries surrounding the heart muscle.

The four main coronary arteries include:

  • right coronary artery (RCA) on the right side of the heart, which supplies blood to the walls of the ventricles and the right atrium
  • left coronary artery (LCA) on the left side of the heart. The left main artery splits into 2 branches:
    • left anterior descending (LAD) artery, which supplies blood to the front of the heart, walls of the ventricles and the left atrium
    • circumflex artery, which supplies blood to the back of the heart, walls of the ventricles and left atrium
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