Functional dyspepsia is one of the most common digestive disorders. The pathophysiology of functional dyspepsia is uncertain. Proton pump inhibitor (PPI) has been recommended as the first line treatment for functional dyspepsia. However, the mechanism of symptom relief is unclear. Most of the previous studies were performed on healthy volunteers who received only a very short course of PPI. The correlation between symptom and gastric emptying is lacking in these studies.