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Cardiovascular system

Your cardiovascular system is a network made up of blood vessels and your heart, which is responsible for pumping blood and oxygen around your body. It also transports carbon dioxide, a waste product, from your body to your lungs – breathing out removes carbon dioxide from your body.

Animation: How your heart works

About your cardiovascular system

Your cardiovascular system is made up of your:

  • heart
  • blood vessels – arteries, veins and capillaries (small blood vessels)
  • blood

How does your cardiovascular system work?

When you breathe in air through your mouth and nose it travels to your lungs. Oxygen from the air is absorbed into your bloodstream through your lungs. Your heart then pumps oxygen-rich (oxygenated) blood through a network of blood vessels (arteries) to tissues including your organs, muscles and nerves, all around your body.

When blood reaches the capillaries in your tissues it releases oxygen, which cells use to function. Cells release waste products, such as carbon dioxide and water, which your blood absorbs and carries away. The used (deoxygenated) blood then travels through your veins and back towards your heart. Your heart pumps the deoxygenated blood back to your lungs, where it absorbs fresh oxygen, releases the carbon dioxide and the cycle starts again.

Your heart

Your heart is roughly the size of a clenched fist. It lies just to the left side of the centre of your chest (thorax) and is surrounded by a protective membrane called the pericardium.

Your heart is a pump, divided into left and right sides. It has walls, made of muscle, which squeeze (contract) to pump blood into your blood vessels and around your body. You have around 8 pints of blood in your body, and in an average day your heart beats about 100,000 times to keep your blood circulating.

Your veins deliver deoxygenated blood from your body to the right side of your heart. Your heart pumps this blood back to your lungs, where it absorbs more oxygen. This oxygenated blood then returns to the left side of your heart, which pumps it out to the rest of your body through your arteries. The muscle on the left side of your heart is slightly larger because it has more work to do than the right – the right side only pumps blood to your lungs, the left side pumps blood around your whole body.

Each side of your heart is divided into an upper chamber called an atrium and a larger, lower chamber, called a ventricle. Blood flows from each atrium to the ventricle below, through a one-way valve.

Image showing the main organs, arteries and veins in the cardiovascular system.

Your lungs

You have two lungs that are positioned on either side of your heart in your chest. Your lungs are made of spongy tissue with a rich blood supply. Air passes from your nose and mouth into your trachea (windpipe), before passing into each lung, through two airways called the bronchi. These divide into smaller airways, called bronchioles, which repeatedly divide and end in tiny sacs called alveoli. It's here that oxygen and carbon dioxide filter into and out of your blood across a thin membrane. In this process, oxygen and carbon dioxide bind to haemoglobin, which is a protein in your red blood cells.

Your diaphragm is a sheet of muscle that separates your chest from your abdominal cavity and forms the floor of your thorax. Downwards movement of your diaphragm as you breathe in makes your lungs inflate. In an average day, you breathe 10,000 litres of air in and out of your lungs.

Your blood pressure

Your blood pressure is an important part of how your cardiovascular system works. Your blood carries oxygen and nutrients and is pumped around your body by your heart. The blood is under pressure as a result of the pumping action of your heart and the size and flexibility of your arteries.

When your blood pressure is measured, the result is expressed as two numbers or levels. Your blood pressure is measured in mmHg, or millimetres of mercury. A blood pressure reading shows one number on top of another, such as 120/80mmHg (one hundred and twenty over eighty millimetres of mercury).

The first figure is called the systolic blood pressure. This is a measure of the pressure when your heart muscle is contracted and pumping blood out of your heart, and is the maximum pressure in your blood vessels. The second figure is called the diastolic blood pressure. This is the pressure between heart beats when your heart is resting and filling with blood, and is the minimum pressure in your blood vessels.

Generally, the lower your blood pressure, the better it is for your health, although very low blood pressure can make you feel dizzy or cause you to faint. For people under the age of 80, doctors recommend your blood pressure is kept below 140/90 measured in a clinic, or 135/85 measured at home. A slightly higher level is acceptable for people over 80. If you have diabetes, kidney disease or cardiovascular disease, your blood pressure should be lower than this – ideally less than 130/80.

The only way to know what your blood pressure is, and whether it’s at a healthy level, is to see a doctor or nurse, who will arrange to check all your cardiovascular risk factors and carry out other tests such as 24 hour blood pressure monitoring.

Your cardiovascular health

Your lifestyle plays an essential part in maintaining your long-term cardiovascular health. Eating a healthy diet, getting plenty of exercise and not smoking can all help you to maintain a healthy cardiovascular system.


Produced by Krysta Munford, Bupa Health Information Team, December 2012.

For answers to frequently asked questions on this topic, see FAQs.

For sources and links to further information, see Resources.

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  • This information was published by Bupa's Health Information Team and is based on reputable sources of medical evidence. It has been reviewed by appropriate medical or clinical professionals. Photos are only for illustrative purposes and do not reflect every presentation of a condition. The content is intended only for general information and does not replace the need for personal advice from a qualified health professional. For more details on how we produce our content and its sources, visit the about our health information page.

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