Prolong exposure of acid to the esophageal squamous epithelium results in development of carditis, an acid-induced mucosa injury at the distal end of the esophagus. After effective antireflux surgery, abnormal esophageal acid exposure is eliminated. Little is known about the effect of the acid reduction on the injured tissue after a surgical antireflux procedure. The aim of this study was to investigate the effect of antireflux surgery on cardiac mucosa (CM) and carditis. Methods: Study population consisted of 61 consecutive patients who had antireflux surgery with pre and postoperative GEJ biopsies. All had CM prior to surgery. Patients with intestinal metaplasia (IM) on preoperative biopsies were excluded. Pre and postoperative biopsies were reviewed to determine changed CM. Regression of CM was defined when conversion from CM to oxyntocardiac mucosa (OCM) or oxyntic mucosa (OM) occurred. Non-regression of CM was unchanged or progressed to IM. Age, sex, 24hr pH study and endoscopic findings of the fundoplication were compared between non and regression groups. Results: At a median of 20 months after surgery, the prevalence of cardiac mucosa was significantly decreased compared to matched preoperative biopsies (p=0.001). Severity of inflammation of columnar lining esophagus was also lower in postoperative biopsies (p=0.01). Regression of CM was demonstrated in 18 (29%) patients (17 to OCM, 1 to OM). CM was progressed to IM in 4(6%) and remained unchanged in 39(64%) patients. Thirty-six patients had postoperative 24 hr esophageal pH studies. Of these, 28 had a normal pH test. Of 28 patients, 12(43%) had histologic regression to OCM and 16 remained unchanged. Of 8/36 patients who had positive pH test, 2 had histologic progression to IM and 6 remained unchanged. Given these results, the prevalence of CM regression was significantly higher in pH negative compared to pH positive patients (12/28 vs 0/8, p=0.02). Age, sex, type of antireflux operation and anatomical distortion of fundoplication were comparable between the groups.Conclusions: This study confirms that after antireflux surgery, conversion of cardiac mucosa to oxyntocardiac or oxyntic mucosa occurs in nearly a third. This prevalence is increased to 43% when elimination of esophageal acid exposure was documented. The severity of its inflammation was significantly decreased as well. This evidence implies that acid-related injury to the GEJ is effectively protected after antireflux surgery.