Reflux esophagitis (RE) is characterized by excessive esophageal acid exposure. The number of acid reflux episodes, the way acid comes up after reflux and the delay of acid bolus clearance cause excessive esophageal acid exposure. Transient lower esophageal sphincter relaxation(TLESR) is the major mechanism of acid reflux in both healthy subjects (HS) and in patients with acid reflux disease, but there is no difference in the rate of TLESRs or in the rate of acid reflux during TLESRs above the LES between HS and patients with severe RE. In patients with severe RE, refluxed acid above the LES rises more easily to the proximal esophagus but it does not clear easily from the esophagus when compared with HS. The pathophysiology of non-erosive reflux disease (NERD) is poorly understood, however with regard to esophageal motility in patients with NERD, the LES pressure, the pressure wave amplitude and the rates of successful primary peristalsis were similar to that of HS but the triggering of secondary peristalsis was defective. This may lead to prolonged contact time between refluxed gastric acid and esophageal mucosa thereby leading to symptoms.