The heart is made up of 3 main layers. The outermost layer is the epicardium, a thin membrane that helps to lubricate the heart.

Next is the myocardium: this is the thicker layer of the heart and contains cardiac muscles. These muscles pump throughout your life to send blood all the way around the body. Your heart beats about 100,000 times in one day- in an average human lifetime, it will beat more than 2.5 billion times!

The final layer is the endocardium. This smooth layer lines the inside of the heart and prevents blood from sticking and forming clots.

The heart has 4 main chambers, the left and right atria and the left and right ventricles.

The two atria are the smaller chambers towards the top of the heart. These receive blood from outside the heart and have only a thin layer of myocardium as they do not need to pump blood as far.

The two ventricles are the larger, lower chambers within the heart. The right ventricle pumps blood to the lungs (the pulmonary circuit) while the left ventricle pumps blood to the rest of the body (systemic circuit). If you look closely at the left side of the heart, you can see that the muscle here is much thicker- this is because it needs to contract much more strongly in order to pump the blood all the way around the body!

The beating sound from the heart is made by the valves opening and closing; these valves prevent blood from flowing back in the wrong direction.