How the heart works

The human heart pumps blood to every part of your body. Learn about the different parts of the heart and watch our video about how a healthy heart works.

Your heart is the pump which powers your body. It supplies blood carrying oxygen and nutrients to every cell, nerve, muscle and vital organ in your body.

It sits in your chest between your lungs, slightly to the left of centre, and is protected by your rib cage.

Your heart is about the size of your clenched fist and weighs about 300 grams (that's just over half a packet of butter).

Watch our step-by-step video of how the heart works

What are the parts of the heart?

Your heart is a bit like a house. It has:

• outer walls (the outer muscle or myocardium)
• rooms (chambers)
• doors (valves)
• plumbing (arteries and veins)
• electrics (the electrical conduction system).

Heart walls

The walls of your heart are made of powerful muscle tissue, which squeezes and relaxes to pump blood around your body. This muscle tissue is divided into three layers.

• The endocardium (the inside layer).
• The myocardium (the muscular middle layer).
• The epicardium (the protective outer layer).

Heart chambers (rooms)

Your heart is made up of four chambers, two on the right and two on the left. These are like the rooms of your house.

The top two chambers are called the left and right atrium and the bottom two are called the left and right ventricles.

They are divided by a thin wall called the septum.

Heart valves (the doors between the rooms)

There are four valves that act like doors to keep blood flowing in the right direction. They open and close as your heart pumps.

The valves only open one way. This stops blood flowing in the wrong direction between the chambers of your heart.

The two valves that sit between the upper and lower chambers of the heart are called the atrioventricular, or AV valves.

The tricuspid valve is the door between the right atrium and ventricle.

The mitral valve is the door between the left atrium and ventricle.

The other two valves are the doors out of the ventricles. They are called semilunar, or SL valves.

The aortic valve is the door out of the left ventricle into the aorta.

The pulmonary valve is the door out of the right ventricle into the pulmonary artery.

The blood vessels (the plumbing)

Blood travels between the heart and the lungs and the rest of the body, via a network of pipes called the blood vessels. There are three main types of blood vessels.

• Arteries, which carry oxygenated blood from your heart to the rest of your body.
• Veins, which carry the de-oxygenated blood back to your heart and lungs.
• Capillaries, the small vessels where oxygenated and de-oxygenated blood is exchanged.

How the heart pumps

Your conduction system sends the electrical signals which trigger the heart to pump blood around the body, and to and from the lungs.

Blood which has used all its oxygen is returned to the right side of the heart, via large veins called the inferior and superior vena cava. From there it is pumped to the lungs, via the pulmonary artery.

Once the blood has received oxygen from the lungs, it travels through the pulmonary veins into the left side of the heart. From here it is pumped back out around the body, via the aorta.

The heart's conduction system (the electrics)

Your heart has its own electrical wiring system (conduction system), which keeps it beating. This conduction system includes:

• the sinoatrial (SA) node (or sinus node). This is your body’s own internal pacemaker, that produces electrical signals to make your heart beat
• the atrioventricular (AV) node. This is a node that passes on the electrical signals from the upper chambers of the heart (artia) to the lower ones (ventricles)
• the bundle of His, the left and right bundle branches, and the Purkinje fibres. These act like electrical wiring that communicate the signals around the heart.

The SA node sends an electrical signal that makes the upper chambers of the heart (atria) contract (squeeze). This pushes blood out of the atria and into the lower chambers of the heart (ventricles).

The electrical signal passes from the atria to the AV node. From there, it passes through the bundle of His and into the right and left bundle branches.

Finally, the signal travels down the Purkinje fibres, causing the ventricles to contract. This pushes blood out of your heart to your lungs and the rest of your body.

How the heart pumps

Your conduction system sends the electrical signals which trigger the heart to pump blood around the body, and to and from the lungs.

Blood which has used all its oxygen is returned to the right side of the heart, via large veins called the inferior and superior vena cava. From there it is pumped to the lungs, via the pulmonary artery.

Once the blood has received oxygen from the lungs, it travels through the pulmonary veins into the left side of the heart. From here it is pumped back out around the body, via the aorta.

The coronary arteries

The heart has its own network of blood vessels, which supply it with the blood it needs to keep pumping.

These vessels are called the coronary arteries. They branch off the body’s largest artery, the aorta, and lie on the outside of your heart.

Narrowing in one of the coronary arteries can lead to angina and a blockage can cause a heart attack.

Learn about heart conditions

What is your pulse?

The pulse you can feel, for example in your wrist or neck, is the heart pumping blood. You can measure the rate and rhythm of your heart by taking your pulse.

How to take your pulse