Above is an illustration of a hiatal hernia. The first frame (1) shows normal anatomy. Between 1 and 2 the animation shows formation of the hiatal hernia. Between 2 and 3 shows transient relaxation of the LES and crural diaphragm leading to reflux into the esophagus. Between 3 and 4 shows clearance of the acid from the esophagus by swallow-induced esophageal peristalsis. The acid is cleared partially into the hiatal hernia, where it can lead to reflux if the LES opens (with inspiration, for example, as negative intrathoracic pressure may force open a weak LES and the now separated crural diaphragm can no longer help counteract this) -- shown between 4 and 5.