A double-blind study comparing Esomeprazole Magnesium 40 mg once daily and Lansoprazole 30 mg twice daily to control the symptoms in patients with gastroesophageal reflux disease (GERD) with continued heartburn symptoms with a course of therapy of 30 mg twice daily Lansoprazole.

Inclusion Criteria:

• Subjects must have reported history of heartburn symptoms whilst on lansoprazole 30 mg twice daily during the 30 days prior to screening.
• Subjects must have a minimal cumulative heartburn score of at least 4 for a minimum of 14 days, where zero = none, one = mild, two = moderate, three = severe.

Exclusion Criteria:

• subjects history of esophageal ulcers, esophageal strictures, esophageal neoplasms, gastric or duodenal ulcers, or any other significant gastric or esophageal pathology judged to be clinically significant by the investigator.
• Subjects with persistent heartburn symptoms while on lansoprazole 30 mg twice daily for a period of > 6 months
• Subjects with a history of severe hepatic insufficiency (specifically, Childs-Pugh Class C liver disease) that may adversely affect the metabolism abd pharmacokinetics of esomeprazole and/or lansoprazole.