The cardiac sphincter is a circular muscle located where the lower end of the esophagus joins the stomach, according to Dictionary.com. The muscle serves as a valve that contracts to prevent acid reflux and relaxes to allow food to pass.
A malfunctioning cardiac sphincter sometimes results in gastroesophageal reflux disease, a disease that allows the stomach acid to erode the esophagus, according to the Mayo Clinic. Many people find relief from GERD through medication that reduces the production of stomach acid or lifestyle changes. However, others need medication that strengthens the sphincter muscle. In some cases, surgery is required. The Mayo Clinic reports an FDA-approved surgical implant available as of 2014 is made of bead-shaped titanium magnets that circle the esophagus to enhance the function of the cardiac sphincter. The beads have enough magnetic attraction to keep the esophagus closed most of the time, but they separate to allow food to pass.
In some individuals, the cardiac sphincter does not open enough to allow food to pass into the stomach. With achalasia, the muscles of the esophagus are too weak to force the food forward through the digestive tract and the cardiac sphincter keeps the valve into the stomach closed. While there is no cure for achalasia, the Mayo Clinic recommends endoscopic surgery to manage the condition.