By Sam M, Jordan M and Finn S

The large veins carry the oxygenated blood to your heart which pumps it round your body supplying all your cells with oxygen and food. Blood vessels are tubes that carry the blood to every cell in your body. When the blood has done its work it runs back into the heart via another set of tubes.

Your heart is a muscle. It's located to the left of the middle of your chest, and it's about the size of your fist. The heart muscle is special because of what it does. The heart sends blood around your body. The blood gives your body the oxygen and nutrients it needs. It carries away waste to. Your heart is sort of pump, or two pumps in one. The right side of your heart (the right atrium) receives blood from the body and pumps it to the lungs. The left side of the heart (the left atrium) does the exact opposite: It receives blood from the lungs and pumps it out to the body.

The two chambers on the bottom are called the ventricles. Their job is to distribute the blood to the lungs and body. Running in the middle of the heart is a thick wall of muscle called the septum. The septum's job is to separate the side’s of the heart. The atria and ventricles work together - the atria fills with blood, then dumps the blood into the ventricles. The ventricles then squeeze which pumps the blood out of the heart. While the ventricles are squeezing, the atria will refill and get ready for the next contraction. Your blood relies on four valves inside the heart. A valve lets something in and keeps it there by closing.

Two of the heart valves are the mitral valve and the tricuspid valve. They allow blood flow from the atria to the ventricles. The others are called the aortic valve and pulmonary valve, and they are in charge of controlling the flow as the blood leaves the heart. All these valves all work to keep the blood flowing forward. They open to let the blood move ahead, then they close to keep the blood from flowing backward. Blood doesn't slosh around your body, once it departs the heart. It moves through lots of tubes called veins and arteries, which are called blood vessels. The blood vessels are attached to the heart. The blood vessels that carry blood back to the heart are called veins. The ones that carry blood away from the heart are called arteries.

The movement of the blood through the heart and around the body is called circulation. It takes less than 60 seconds to pump blood to every cell in your body. Your body needs the steady supply of blood to keep it working properly. Blood delivers oxygen to everyone of the body's cells. Without oxygen, these cells would die. If that oxygen-rich blood doesn't circulate, a person could die. Each time the blood circulates from the heart out to the body, around 20% of it goes through the kidneys. The kidneys filter out some of the waste before the blood goes back to the heart. The returning blood enters the right side of the heart. It takes the blood to the lungs for freshening up. Carbon dioxide is left in the lungs to be removed when we exhale. Then another fresh breath of oxygen that can enter the blood to start the process again and it all happens in about a minute!

Heart Attack. A normal heart beats evenly and easily. Damage to the heart can cause it to beat irregularly, which may prevent blood from flowing properly. When the heart malfunctions, this can disrupt or even stop normal breathing. If the heart attack causes the heart to stop beating, this is known as cardiac arrest. Heart disease happens because the excess cholesterol and other fatty deposits are transported in the blood stream and get stuck to blood vessel walls, making them narrower, and in some cases, even blocking them and stopping blood flow. This can also lead to a heart attack. High blood pressure, hypertension, happens when the heart's pumping of blood meets higher-than-normal resistance in the blood vessels outside the heart. It is often doesn’t matter but the resulting overwork can lead to heart failure.

Sudden cardiac arrest occurs when the heart’s electrical system malfunctions. Usually the heart has a rhythmic beat, but when sudden cardiac arrest occurs, the beating becomes more rapid. This results in the lower chambers of the heart, the ventricles, to quiver instead of contract, and they can no longer pump blood from the heart to the rest of the body.  Remember that your heart is a muscle. If you want it to be strong, you need to exercise it. You can do this by being active in a way that gets you huffing and puffing, like running, fighting, or playing rugby. Try to be active every day. Eat a variety of healthy foods and avoid foods high in unhealthy fats, such as saturated fats and trans fats.  Don't smoke. It can damage the heart and blood vessels.