Cardiovascular system

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.

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.

What sorts of exercise can I do to keep my heart healthy?


You can improve the health of your heart (your cardiovascular fitness) and reduce the risk of heart disease, diabetes and stroke through many different types of physical activity or exercise.


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 sustained exercise that gets your heart to work more.

The recommended healthy level of physical activity is at least 150 minutes (two and a half hours) of moderate exercise over a week in bouts of 10 minutes or more. It may help you to think of this as 30 minutes of exercise at least five days a week. Moderate exercise means your breathing becomes faster, your heart rate is increased and you feel warmer. At this level of activity, your heart and lungs are being stimulated and this helps you become fitter.

Good forms of cardiovascular exercise include running, aerobics, cycling and swimming. Your exercise quota can also include all kinds of day-to-day activities such as:

  • gardening
  • climbing stairs
  • walking
  • vacuuming

If you’re 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.

I have diabetes and 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 on how you can reduce your risk by making lifestyle changes and controlling your condition.


If you have diabetes, raised blood sugar levels can increase the risk of your arteries becoming narrowed or blocked. People with diabetes are more susceptible to the other risk factors for cardiovascular disease such as high blood pressure, raised cholesterol and smoking. Therefore, 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 encourage you and offer help for you to stop smoking.

High blood pressure is common in diabetes and it's important to control it. You should aim for your blood pressure to be below 130/80mmHg, or lower 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.

If you have type 2 diabetes, you may have low HDL cholesterol levels (high-density lipoprotein, or 'good' cholesterol) and high triglyceride levels (a type of fat) in your blood. Both these factors can increase the risk of heart disease. To help reduce your cholesterol levels, you may need to take medication. Cutting down on fats in your diet, particularly saturated fats (which are found mostly in red meat and dairy products), will also help.

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

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 heart disease is caused by years of stress. In fact, 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. Common 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 the sources of stress in your life is to keep a diary. Keep a record of when you feel stressed and make notes about situations that make you feel stressed. This might help you work out why you feel more stressed on some days than others. Once you have identified the possible causes of your stress, you can 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 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.

Try talking to friends, colleagues or family members about any worries you have, as sharing a problem 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.