Your heart: The basics
How your heart pumps
Your heart in action
Your heart is a pump. With every beat, it pushes blood around your body and ensures that your cells are supplied with oxygen, nutrients, and everything else they need to survive.
It is quite small – about the size of a closed fist – and, on average, it beats 100,000 times each day.
The animations on this page illustrate what happens when your heart beats and show how blood flows through it.
The right side of the heart is shown in blue: Blue is used to show blood that is low in oxygen. This is blood that is returning from its journey around your body. Your heart pumps this blood to your lungs to be refreshed with oxygen.
The left side is red: Red indicates blood that is high in oxygen. This is blood returning from your lungs to be pumped back around your body.
Your heart is made up of four chambers, two upper chambers, called the atria, and two lower chambers, called the ventricles.
The role of your atria is to take in blood from your body (right atrium) or your lungs (left atrium) and push it into your ventricles, which are the heart’s lower chambers. The atria are important because they function as reservoirs, supplying blood for your ventricles.
Your ventricles pump blood through to your lungs (right ventricle), for re-oxygenation, or out to your body (left ventricle), to keep you alive and well. Your ventricles do most of your heart’s hard pumping work.
Your heart in one beat
Blood flow within your heart is controlled by four valves that open to let blood enter the atria and ventricles and then close to prevent back-flow on contraction. The four valves are called the aortic valve, the mitral valve, the pulmonary valve, and the tricuspid valve.
Your heart is controlled by an internal electrical system that coordinates all the muscles to get them to work together. It also controls the rate at which your heart beats.
At rest, your heart rate is slower than it is when you’re exerting yourself. If you’re exercising, it can go up considerably.
To learn more about this take a look at Your heart’s electrical system.
Where is your heart?
Your heart is roughly in the middle of your chest, slightly to the left of center.
It is connected to your circulatory system, which is the network of arteries, veins, and capillaries that takes blood to and from every part of your body.
To learn more, take a look at Your circulatory system, where we explain where your blood goes when it leaves your heart.