How the heart works

The human heart pumps blood to every part of your body. Learn to identify the different parts of the heart and watch our video about how a healthy heart works.

Your heart is part of your circulatory system and pumps blood through your blood vessel network to all the muscles and vital organs in your body.

Every part of the heart works together to make sure your heart functions properly.

Parts of the heart

Your heart is a powerful muscular organ in the left side of your chest between your lungs and is protected by your rib cage. It is about the size of your clenched fist.

Most of your heart is covered by three layers: an inner muscle layer called the myocardium; then a membrane layer called the epicardium; then the outer pericardium protective sac.

Your heart gets the oxygen and food it needs to pump blood through its own blood vessel network called the coronary arteries.

Watch our step-by-step video of how the heart works

Heart chambers

Your heart is made up of four chambers. The top two chambers are called atria and the bottom two are called ventricles. The ventricles have thicker, more muscular walls than the atria because they have to pump blood further.

Blood lacking in oxygen enters the heart through the right atrium (from the vena cava) and then flows into the right ventricle. It is pumped to the lungs (via the pulmonary artery) where it collects oxygen. Oxygen-rich blood from the lungs flows back to the heart (via the pulmonary vein) and arrives in the left atrium. This blood flows from the left atrium into the left ventricle, where it is pumped out to the rest of the body (via the aorta).

Heart valves

There is a valve at the exit of each room in your heart. A valve is a flap-like structure that works like a one-way door, opening and closing as your heart beats. This makes sure blood flows in only one direction through your heart.

The heart has four valves. Two sit between the atria and ventricles (atrioventricular or AV valves), and two sit at the base of the arteries connected to the ventricles (semilunar or SL valves).

Tricuspid valve: The right AV valve is made up of three flaps and prevents blood flowing back into the right atrium from the right ventricle.

Mitral valve: The left AV valve is made up of two flaps. It stops blood flowing back into the left atrium from the left ventricle.

Aortic valve: The right SL valve is at the base of the aorta and prevents blood flowing back into the left ventricle.

Pulmonary valve: The left SL valve is at the base of the pulmonary artery (which leads to the lungs) and prevents blood flowing back into the right ventricle.

How the heart pumps

Your heart pumps blood using its own electrical conduction system. This system is made up of three main parts, also known as conduction nodes: the sinoatrial (SA) node, the atrioventricular (AV) node, and the His-Purkinje system.

Each time your heart pumps, it sends blood through the heart chambers, into the lungs and around the body. During this cycle your heart’s ventricles relax (diastole) and squeeze (systole) to pump blood and your heart valves open and close.

The SA node (generator) sends out an electrical signal. This signal makes cells in the atria squeeze, pumping blood into the ventricles.

The signal travels to the AV node and slows briefly to allow your ventricles to fill with blood.

The signal follows a pathway called the Bundle of His down the Purkinje fibres (these are like your heart’s electrical wiring) to your ventricles.

The signal makes cells in the ventricles squeeze and the heart beats, pumping blood out of the heart.

The ventricles relax and wait for the next signal.

Your heart’s electrical impulses can be recorded using an ECG (electrocardiograph).

Find out what can go wrong with the heart

What is your pulse?

The pulse you can feel, for example in your wrist or neck, is the heart pumping blood. You can measure the rate and rhythm of your heart by taking your pulse. The rate is the speed your heart beats, which is recorded in the number of beats per minute. The rhythm is the regularity of the interval between the beats. 

Sometimes your pulse will be faster or slower, depending on your health and whether you have exercised or are resting.