how does the heart beat? before each beat, your heart fills with blood. then it contracts to squirt the blood along. when something contracts, it squeezes tighter - try squeezing your hand into a fist. that's sort of like what you heart does so it can squirt out the blood. your heart does this all day and all night, all the time. everyday , an adult heart pumps 2,000 gallons ( 7,500 liters) of recycled blood by filling and contracting. the heart is one tough worker