The bottom of your heart rests on your diaphragm. The top of your heart sprouts a thick tangle of large tubes. Your heart is shrouded at the moment by a sac of tissue, a membrane called the pericardium, which acts like bubble wrap by both protecting your heart and holding it in place. Peel away this sac. Inside is a watery lubricant that minimizes friction when your heart beats. Shooting down from the aorta—the large tube arching on top of your heart—are two large arteries that branch out like lightning forks over the heart muscle.
