Trial of IW-3718 for 8 Weeks in Patients With Persistent Gastroesophageal Reflux Disease (GERD) Receiving Proton Pump Inhibitors (PPIs)

Inclusion Criteria: Each patient must meet all of the following criteria to be eligible for enrollment in this study: * Patient is an ambulatory male or female (if female, nonpregnant) and is at least 18 years old at the Screening Visit. * Patient has a diagnosis of GERD and reports experiencing GERD symptoms (heartburn or regurgitation) while taking standard PPI therapy. * Patient has evidence of pathological acid reflux. * Female patients must not be pregnant and must agree to avoid pregnancy for the duration of the study. * Patient must comply with study procedures. Exclusion Criteria: Patients who meet any of the following criteria will not be eligible to participate in the study: * Patient has a history of complete lack of GERD symptom response to PPI therapy. * Patient has a significant medical or surgical history including conditions that would impact drug absorption or metabolism (such as bowel obstruction, poorly controlled diabetes, gastroparesis, hiatal hernia). * Patient reports pain or burning behind the breastbone or in the center of the upper stomach as his or her predominant symptom at the Screening Visit. * Patient has received an investigational drug during the 30 days before the Screening Visit, or is planning to receive another investigational drug or use an investigational device at any time during the study. NOTE: Other inclusion and exclusion criteria apply, per the study protocol.