Your heart is a pump made of muscle which pushes blood through your arteries to all organs of your body. The body needs oxygen and energy to work normally and blood is the delivery system. Blood picks up its oxygen in the lungs and becomes bright red as a result. After it gives up its oxygen, blood takes carbon dioxide and waste products for elimination to the lungs, liver and kidneys in the veins, where it is a now a dark red colour. Your heart muscle needs oxygen and energy and this is obtained from the blood through the coronary arteries. Disease of the coronary arteries is the commonest cause of death and disability in the western world because it stops the heart – the body’s engine – doing its job properly.