How your heart works

The human heart works like a pump sending blood around your body.

It’s a muscle, about the size of your fist, in the middle of your chest tilted slightly to the left.

Function of the heart

Each day, your heart beats around 100,000 times. This continuously pumps about 5 litres (8 pints) of blood around your body through a network of blood vessels (called arteries and veins) in your circulatory system.

This blood delivers oxygen and nutrients to all parts of your body to help your organs and muscles work properly. Your blood also carries away unwanted carbon dioxide and waste products.

Structure of the heart

Your heart has 4 important areas: 

Chambers of the heart

Your heart has a left side and a right side. They are separated by a thin muscular wall called the septum. Both sides have an upper chamber and lower chamber:

• the 2 upper chambers are called the left atrium and the right atrium (or the atria), they receive blood flowing into the heart
• the 2 lower chambers are called the left ventricle and the right ventricle (or the ventricles), they pump blood out of the heart.

Learn more about how blood flows through the chambers of the heart.

Layers of the heart

Your heart is made up of 3 layers of muscle tissue:

• pericardium, a thin, outer lining that protects and surrounds your heart
• myocardium, a thick, muscular middle layer that squeezes (contracts) and relaxes to pump blood out of the heart to the rest of your body
• endocardium, a thin, inner layer that makes up the lining of the 4 chambers and the valves in your heart.

Valves of the heart

Your blood flows around your heart and the rest of your body in one direction, like a one-way traffic system. Your heart valves control the direction of your blood flow. They act like doors that open and close with every heartbeat. You might hear heart valves called leaflets or cusps.

There are 4 valves in your heart:

• the tricuspid valve is found between the right atrium and right ventricle. It prevents blood from flowing back into the right atrium when the right ventricle contracts
• the pulmonary valve is found between the right ventricle and the pulmonary artery. It prevents blood from flowing back into the right ventricle after it has been pumped to the lungs
• the mitral valve is found between the left atrium and left ventricle. It prevents blood from flowing back into the left atrium when the left ventricle contracts
• the aortic valve is found between the left ventricle and the aorta. It prevents blood from flowing back into the left ventricle after it has been pumped to the aorta to go to the rest of the body.

Coronary arteries

Your coronary arteries supply the heart muscle with blood high in oxygen. They branch off your aorta, which is the main artery in your body.

When your coronary arteries become narrowed by fatty material in their walls, you develop coronary artery disease (also known as coronary heart disease).

If a piece of the fatty material breaks off, a blood clot (clump of blood) forms around this to try and repair the damage to the artery wall. This clot can block your coronary artery and cut off the supply of blood and oxygen to your heart muscle. This is known as a heart attack.

Electrical conduction system of the heart

Your heart has an electrical conduction system which sends signals throughout the upper chambers (atria) and lower chambers (ventricles). The electric signals make your heart beat in a regular, coordinated rhythm.

The electrical signals are sent from a group of cells called the sinus node which is known as your heart’s natural pacemaker. Usually, the sinus node will send the electrical signals at a steady pace, but the pace can change depending on your emotions and if you are active or resting. The speed at which your heart beats is also known as your heart rate. 

Circulatory system

Your heart is linked to the rest of the circulatory system with blood vessels (tubes) called arteries and veins:

• your arteries deliver blood high in oxygen from the heart to other areas of your body
• your veins return the blood low in oxygen from your organs back to your heart
• your arteries and veins are connected by even smaller blood vessels called capillaries.

How does blood get oxygen?

Your blood flows through your heart and your lungs to pick up oxygen before being pumped to the rest of your body. Oxygen is added to your blood in 4 main steps:

• the right atrium receives blood low in oxygen from the rest of the body. It pumps the blood to the right ventricle
• the right ventricle pumps the blood low in oxygen to the lungs to pick up a fresh supply of oxygen
• the left atrium receives blood high in oxygen from the lungs and pumps it to the left ventricle
• the left ventricle pumps blood high in oxygen to the rest of the body.

Heart and circulatory diseases

Sometimes the heart and circulatory system do not work like they should. This can cause heart and circulatory diseases (also sometimes called cardiovascular diseases). There are many heart and circulatory diseases, including:

• coronary heart disease
• heart attack
• angina
• cardiac arrest
• arrhythmias
• congenital heart disease
• inherited heart conditions
• stroke
• vascular dementia
• type 2 diabetes.

Causes of heart and circulatory diseases

There are different things that increase your risk of heart and circulatory diseases. This includes:

• type 2 diabetes
• high blood pressure
• high cholesterol
• having excess weight
• smoking
• drinking too much alcohol
• getting older
• your assigned sex at birth.

Heart Helpline and other support

Heart Helpline & other support:

• Contact our Heart Helpline to speak to one of our cardiac nurses.
• Join our online community HealthUnlocked to connect with others who are affected by a heart condition.
• Sign up to our Heart Matters magazine and online information packed with health and lifestyle advice.