OBJECTIVES: Gastroesophageal reflux can occur because of low resting pressure, transient relaxation, or normal relaxation of the lower esophageal sphincter. Mechanisms for delayed esophageal clearance include impaired peristalsis, infrequent swallowing, and impaired sphincter relaxation. The purpose of this study was to examine esophageal function in patients with gastroesophageal reflux and to determine esophageal acid clearance. METHODS: Esophageal contractile pressure, duration, velocity, pH, sphincter pressure, and deglutition were monitored in 12 heartburn patients 1 h before and 3 h postprandially twice. RESULTS: Eighty-seven episodes of gastroesophageal reflux occurred during normal sphincter relaxation, and 72 episodes occurred during transient sphincter relaxation; however, the frequency with normal sphincter relaxations was quite low (1%) compared with transient sphincter relaxations (33%). Mean and median esophageal acid exposure was not different during normal sphincter relaxation (71 and 80 s) compared with during transient sphincter relaxation (71 and 81 s). There were 284 instances of primary peristalsis, with 157 resulting in esophageal acid clearance, compared with simultaneous contractions (6 of 66), secondary peristalsis (1 of 7), and tertiary contractions (0 of 45). Contractile pressures were higher and durations were longer with acid clearance, but velocities were not different. CONCLUSIONS: Frequency of gastroesophageal reflux is the same during normal and transient sphincter relaxation in heartburn patients. Primary peristalsis is necessary to accomplish acid clearance. Secondary peristalsis is rare and ineffective.