The Maryland Virtual Patient (MVP) Project seeks to create realistically functioning virtual humans endowed with automatic physiological and cognitive function that can be used in the training of medical personnel. Physiologically, the state of an MVP changes in response to internal pathophysiological stimuli and external stimuli, the latter initiated by either by the patient or the trainee. Cognitively, the MVP can communicate with trainees about current symptoms, lifestyle, history, adherence to prescribed treatments, etc. We will demonstrate simulation in the MVP environment using the example of patients suffering from gastroesophageal reflux disease (GERD).