Your heart sits in the middle of your chest and pumps blood from about 4 weeks after conception until the day that you die. It never stops, and over your lifetime it will pump ~175 million liters of blood. To visualize that, imagine the amount of water that falls over Niagara falls in a few minutes. Remarkable! This little pump is the size of your clenched fist and in an adult can weigh about 300 grams. Watch these videos to learn more about how the heart works, blood flow in arteries and veins, and blood pressure.