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Introducing the cardiovascular system

A constant supply of oxygen is needed to keep the body functioning. The cardiovascular system - made up of heart, lungs and blood vessels, and the blood that circulates through these - is responsible for getting oxygen into your body, and circulating it everywhere its needed.

This information was published by Bupa's health information team and is based on reputable sources of medical evidence. It has been peer reviewed by Bupa doctors. The content is intended for general information only and does not replace the need for personal advice from a qualified health professional.  

cardiovascular system

Oxygen enters the body through your mouth and nose, and is breathed into the lungs, where its absorbed into the blood. The heart then pumps this oxygen-rich blood through a network of blood vessels, your arteries, to tissues - organs, muscles and nerves - all around the body.

When blood reaches these tissues, it releases the oxygen, which is then used to produce energy. In exchange, the tissues give up waste products - including carbon dioxide and water - which are, in turn, absorbed and carried away by blood.

This used - or deoxygenated - blood then travels along veins, back towards your heart. Your heart pumps this blood back to your lungs, where it picks up fresh oxygen, and starts the cycle once again.



An adult humans heart weighs about 300g, and is roughly the size of a clenched fist. It lies in the centre of the chest, surrounded by a protective membrane called the pericardium. In an average day, it pumps nearly 8,000 litres of blood.

Its a muscular organ, divided vertically into left and right sides. The left side is slightly larger because it has more work to do.

The right side of the heart receives deoxygenated blood from elsewhere in your body. It pumps this blood to the lungs, to pick up more oxygen. This oxygenated blood then returns to the left side of the heart, which pumps it out to the rest of your body.

Each side of the heart is further divided into an upper chamber - or atrium - and larger lower chamber, called a ventricle. Blood flows from the atria to the ventricles through a one-way valve. Your heart works like a pump, with its muscular walls contracting to force the movement.

At rest, a healthy adult breathes between six and seven litres of air into the lungs every minute. These lungs consist of spongy tissue - that flank the heart in the chest cavity (thorax).

The diaphragm - a sheet of muscle, which separates the chest from the abdominal cavity - forms the floor of the thorax. Its responsible for inflating and deflating the lungs as you breathe.

From the nose and mouth, air passes into the trachea (windpipe) - through the larynx - or voice box - and into each lung, through two airways called your bronchi. These divide into smaller airway - called bronchioles - which divide again, into alveoli. These are air sacs with walls just one cell thick - its here that the gases oxygen and carbon dioxide can filter into and out of the blood. This process - known as gaseous exchange - involves molecules of oxygen and carbon dioxide binding to haemoglobin, one of the components of your blood.

There are about seven million alveoli in your lungs, providing a vast surface area - around the size of a tennis court if opened out - where gas exchange can take place.

This whole system depends on a process of circulation.

Basically, deoxygenated blood flows towards your heart through two large veins, called the venae cavae. As your right atrium contracts - with the beating of your heart - your tricuspid valve opens, and this deoxygenated blood flows straight into your right ventricle. Your right ventricle then contracts - the second phase of a heart beat - and the tricuspid valve shuts, while the pulmonary artery opens.

The deoxygenated blood is pumped out of your right ventricle, and down your pulmonary artery towards your lungs. Before your next heart beat, your pulmonary valve closes to prevent this blood flowing back into your heart.

When it reaches your lungs, your blood is replenished with oxygen, before being sent back towards your heart, through your pulmonary vein and into your left atrium. On this side of your heart, its the mitral valve which controls blood flow.

This shuts behind the blood, and then your bicuspid valve opens to allow the blood to be pumped from your left ventricle into your aorta, and off on its way round the rest of your body.

From your aorta, numerous arteries divide into smaller arterioles. Eventually, the blood arrives in the smallest vessels - the capillaries. These allow exchange of oxygen, carbon dioxide and other waster products between the blood and the tissues.

Deoxygenated blood is then conveyed in small, then larger, veins back towards your heart for the whole cycle to begin again. All along the way, one-way valves prevent the backflow of blood in your veins.

As blood travels around the body, it is under pressure. This pressure can be measured - usually in the brachial artery in your arm.

Blood pressure is expressed. The top figure - or systolic reading - is a measure of the pressure in your artery when the heart is contracting and squeezing blood out. The bottom figure - the diastolic reading - is the pressure when your heart is filling.

Like all muscles, your heart requires a regular supply of blood. This is delivered by your left and right coronary arteries. Its when these become furred up with a fatty deposit called plaque that your heart muscle stops receiving enough blood to work properly.

The result can be:

  • Angina
  • High blood pressure
  • Heart attack
  • Heart failure


See separate facts sheets on these topics.

Your lifestyle over the long term plays an essential part in maintaining cardiovascular health. Follow our tips for keeping the risks to a minimum:

If you smoke, give up - smoking causes serious damage to your heart and blood vessels

Exercise regularly - preferably, most days. This does not mean you have to join a gym - moderate intensity activity, such as brisk walking, should be enough

Eat healthily - a healthy diet is high in complex carbohydrates (bread, pasta, potatoes, rice) and fruit and vegetables, and low in saturated fat.

1. What sorts of exercises can I do to keep my heart healthy?

You can improve the health of your heart (your cardiovascular fitness) through different types of physical activity or exercises.

The best kind of exercise for your heart is aerobic activity – this means that it involves or improves the use of oxygen by your body. This is essential for improving your cardiovascular fitness. Aerobic activity can be any repetitive exercise that involves the large muscle groups of your legs, shoulders or arms.

The recommended healthy level of physical activity is 150 minutes (two and a half hours) of moderate exercise over a week in bouts of 10 minutes or more. Moderate means your breathing is faster, your heart rate is increased and you feel warmer. At this level of activity, your heart and lungs are being stimulated and this goes towards making you fitter.

Good forms of cardiovascular exercise include running, aerobics, cycling and swimming. It's important to realise that exercise can also include all kinds of day-to-day activities such as:

  • gardening
  • climbing stairs
  • walking
  • vacuuming

If you are overweight or have a medical condition, check with your GP before starting an exercise programme. He or she will be able to advise you on the best way to increase your physical activity.

2. I have diabetes and I have heard this can affect my heart. Do I need to take special precautions?

If you have diabetes, you have a higher risk of developing heart disease. However, your GP can advise you how you can reduce your risk by making lifestyle changes and controlling your diabetes.

If you have diabetes, you're more likely to have high blood pressure and high levels of fats in your blood. Diabetes can also affect the heart muscle itself, making it a less efficient pump and making it more likely that you will develop heart disease. So, if you have diabetes, your GP will probably prescribe medicines to treat some of the risk factors that you may have. For example, he or she may give you medicines to lower your blood pressure and cholesterol level or aspirin to reduce the risk of blood clotting. If you smoke, your GP will also encourage you to stop smoking.

If you have high levels of triglycerides (a type of fat) and cholesterol in your blood, you have a greater risk of heart disease. The risk is particularly high if you also have a low level of HDL cholesterol (high-density lipoprotein, or 'good' cholesterol), which is more likely if you have diabetes. You may need to take a medicine known as a statin to reduce your cholesterol levels, and you may also need to have another medicine to control your triglyceride levels. Cutting down on fats in your diet, particularly saturated fats (which are found mostly in meat and dairy products), will also help.

High blood pressure is common in people with diabetes and it's important to control it. If you have diabetes, you should aim to have a blood pressure below 130/80mmHg, or lower than that if your kidneys are already damaged. You may be able to control your blood pressure by losing excess weight, doing more exercise and cutting down on alcohol and salt, although you may need to take medicines too.

Being physically active may help to reduce the amount of medicine or insulin you need to take for your diabetes, and can help reduce the risk of heart disease. It's important to monitor your blood glucose carefully as you start to build up your level of physical activity because you may need to change the dose of your medication. Your GP can advise you about this.

3. Can too much stress in my life really cause heart disease?

Stress isn't the only cause of heart disease but when combined with other risk factors, such as smoking, lack of physical activity, and high blood cholesterol, it can act to increase your risk of developing it.

Many people think that heart disease is caused by years of stress. However, there is no evidence to show that stress alone causes heart disease, even though stress can cause your blood pressure to increase.

However, the way you try to cope with stress may increase your risk of developing heart disease. Stress can encourage less healthy behaviour, such as smoking, drinking too much alcohol, and over-eating.

Sources of stress can include relationships, work, health, financial problems, and major events such as moving house, bereavement or divorce.

A good way of identifying your sources of stress is to keep a diary and write in it when you are feeling stressed. This might help you to work out why you feel more stressed on some days than others. Once you have identified the possible causes of your stress, you can then take steps to tackle them and change how you respond to stressful situations.

If you can't change a source of stress, aim to try and change your attitude towards it. Think about how you respond when you find yourself in a stressful situation. Then try and think about how you could change both your physical and mental response to it.

A balanced diet and regular physical activity can help you to feel more ready to cope with potentially stressful situations. It's also important to learn how to relax – yoga and other relaxation techniques may help.

Talking to friends, colleagues or family members about any worries you have can help. If you think you are stressed or very anxious, talk to your GP who will be able to help you decide on the best way to deal with it.

Further information


  • The heart – technical terms explained., accessed 23 September 2010
  • The way your lungs work. British Lung Foundation., accessed 23 September 2010
  • Simon C, Everitt H, van Dorp F. Oxford handbook of general practice. 3rd ed. Oxford: Oxford University Press, 2010
  • Blood pressure. British Heart Foundation., accessed 23 September 2010
  • CVD risk assessment and management. Clinical Knowledge Summaries., accessed 23 September 2010
  • Physical activity and your heart., accessed 23 September 2010
  • Start active, stay active: a report on physical activity from the four home countries’ Chief Medical Officers. Department of Health, 2011.
  • Diabetes. British Heart Foundation., accessed 25 September 2010
  • Diabetes – type 2. Clinical Knowledge Summaries., accessed 25 Septemeber 2010
  • Cardiovascular disease. Diabetes UK., accessed 25 September 2010
  • Coping with stress. British Heart Foundation., accessed 25 September 2010

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