Your heart is amazing. It pumps blood around your body all day and all night. Your blood takes lots of useful things to the cells around your body, such as oxygen and sugar, and removes waste products, like carbon dioxide. Blood is vital, and so is your heart.
The heart is made up of two pumps. The one on the right pumps blood to your lungs, whilst the bigger left pump pumps the blood around your body. Your cells need oxygen from the air to make energy in a reaction called respiration. Respiration produces carbon dioxide as a waste product, so your body needs to get rid of that too. Your heart and lungs work together to make sure that your blood is able to move around your body, and can get new oxygen and get rid of carbon dioxide.
The heart itself is made up of muscles, called cardiac muscles. Cardiac muscles keep beating continually, so long as they are supplied with blood (if you take a cardiac muscle out of a body and bathe it in blood, you’ll see it beating away). So your heart needs its own blood supply. This blood is supplied by coronary arteries.
A heart attack happens when a coronary artery gets blocked. This means that some of the cardiac muscles do not get the blood supply they need and stop beating; sometimes those muscles might even die. One of the main ways that a coronary artery can get blocked is by cholesterol, a kind of fat. This is why heart attacks commonly occur in people who are overweight or obese.