Dysfunction of the lower esophageal sphincter (LES) could result in various gastrointestinal disorders.However, minimally-invasive technology for direct, long-term, ambulatory monitoring of the dynamics of the LES is lacking. This thesis aims at filling this void by presenting a novel, catheter-based acoustic interrogation device for real-time monitoring the motility dynamics of the LES. The device was first tested in-vitro on a custom-designed LES simulator. Measurements showed statistically significant Pearson correlation coefficients (p<0.05). In a pilot test on a canine model, the device successfully detected an episode in which the LES was forced opened and closed by a transoral endoscope, which was monitored by a second, transpyloric endoscope positioned in the distal stomach. The dynamics of the LES was independently confirmed by frame-by-frame endoscopic video analysis. The proposed acoustic catheter has the potential for facilitating the diagnosis of LES-related diseases.