BACKGROUND Systolic anterior motion (SAM) is the dynamic anteriorly directed movement of the anterior mitral valve leaflet during systole toward the left ventricular outflow tract (LVOT). The history of SAM in progressive hypertrophic cardiomyopathy (HCM) is unclear. It is believed that SAM is an irreversible process that progresses as the gradient over the LVOT increases. We present a case where SAM regressed after extensive left atrial (LA) and left ventricle (LV) remodeling in a patient with progressive HCM. CASE REPORT A 78-year-old woman presented with effort dyspnea. Echocardiogram revealed HCM with an interventricular septal (IVS) thickness of 20 mm, significant pressure gradient over LVOT, and prominent SAM. The LV chamber dimensions were within normal range. The patient was prescribed medications against heart failure and discharged. Six years later, she was admitted with an acute respiratory infection. She underwent transthoracic and transesophageal echocardiograms, which showed no systolic function change. The IVS thickness was lower, LV and LA were significantly enlarged, and there was a significant mitral regurgitation with an anteriorly directed jet and no SAM. The transesophageal echocardiogram revealed a posterior leaflet's prolapse with a flail P2 segment, which required percutaneous edge-to-edge mitral repair. CONCLUSIONS Our case highlights the multiple theories behind the mechanism of SAM in HCM. The long-standing pressure gradient over the LVOT lead to extensive left side remodeling, which then altered the geometric, kinetic, and structural forces and, consequently, the Venturi effect. At the end stage of HCM, IVS lost its thickness, pressure gradient declined, and SAM regressed.