BACKGROUND AND AIM: During peroral endoscopic myotomy (POEM) for achalasia, endoscopic esophagogastric junction (EGJ) opening is generally considered a sign of successful myotomy. However, in clinical practice, the EGJ may appear to open immediately after submucosal tunneling, even before myotomy is performed. We defined this phenomenon as pseudo-dilation and evaluated changes in EGJ appearance during POEM. METHODS: This retrospective study included 65 consecutive patients who underwent POEM between February and June 2025. Endoscopic images obtained at three stages-before POEM, after submucosal tunneling, and after myotomy-were evaluated using a three-tier Endoscopic Junctional Dilation (EJD) grade. Differences in EJD grade across procedural stages were analyzed using the Friedman test, with post hoc Wilcoxon signed-rank tests and Bonferroni correction. The Bickenböller statistic was used as a complementary analysis. Two certified endoscopists independently evaluated all images, and interobserver agreement was assessed using Cohen's κ and weighted κ. RESULTS: The EJD grade increased significantly after submucosal tunneling compared with before POEM (p < 0.001). A significant difference was observed between the post-tunneling and post-myotomy stages (p = 0.002); however, most patients showed no change in EJD grade, and the overall distribution of grades remained unchanged (p = 0.124). Overall, pseudo-dilation occurred in 95.4% of patients. Interobserver agreement in EJD grade assessment was substantial to perfect across all procedural stages (κ = 0.889; weighted κ = 0.940). CONCLUSION: Pseudo-dilation of the EGJ was commonly observed immediately after submucosal tunneling during POEM. TRIAL REGISTRATION: N/A.