The human heart, the size of a fist and the strongest muscle in the human body, beats about 100,000 times a day or about 2.5 billion times over a 70 year lifetime. With each beat, blood is pumped from the left chambers of the heart throughout the body, delivering oxygen and nutrients, and collecting waste products, then returning to the right chambers of the heart. Waste products are removed as the blood circulates through the liver.