A laser-induced scar at the cardia increases the yield pressure of the lower esophageal sphincter Low yield pressure of the lower esophageal sphincter is associated with esophageal reflux, and fundoplication must increase yield pressure if it is to prevent reflux. We attempted to increase yield pressure endoscopically in the dog by using the Nd:YAG laser to produce a fibrous scar at the cardia in the approximate line of the gastric sling fibers. Ten beagle dogs were studied. In a pilot study with two dogs, 15 watts for 4.2 sec were found to produce a scar deep into the muscle coat of the stomach. Three configurations of scar were used. One produced significant rises in yield pressure in all four of the dogs treated, the second produced a significant rise in one of the two dogs treated, and the third caused a significant drop in yield pressure in the one dog treated. One dog died of gastric perforation 10 days after lasering, but no other animal experienced any ill effects. These findings may have therapeutic implications for the management of esophageal reflux. 