Ba-boom, ba-boom, ba-boom . . . your incredible heart beats more than once every second, no matter what you're doing. And your lungs pull in up to 145 gallons of oxygen each day. So how are your heart and lungs connected, and what do they do? Join the Stickmen as they explore your body to find out how your heart pumps blood, how oxygen travels through your body, and how your body fights off germs. You'll discover why you need two trillion red...