Study Comparing Esomeprazole Magnesium 40mg Once Daily Versus Lansoprazole 30 mg Twice Daily in Symptom Control of Subjects With Persistent Gastrooesophageal Reflux Disease (GERD)

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.