The heart beats about 2.5 billion times over the average lifetime, pushing millions of gallons of blood to every part of the body. This steady flow carries with it oxygen, fuel, hormones, other compounds, and a host of essential cells. It also whisks away the waste products of metabolism. When the heart stops, essential functions fail, some almost instantly. Find out how your heart works and how the heart and blood vessels change with age. Read about what heart disease is, and get some tips on how to prevent it.