Ischemic mitral regurgitation (IMR) is a common complication, which is accompanied by myocardial infarction, causing heart failure and leading to poor prognosis. Although several surgical techniques have been reported, certain surgical methods have not been established for treating IMR. We report a successful case of left ventricular posterior wall plication through a left atriotomy over the mitral valve for IMR in a patient who experienced cardiac shock and could not be weaned off mechanical support. Posterior wall plication changed the left ventricle from a spherical to an oval shape, restored the position of papillary muscles and posterior wall, improved leaflet tethering, and prevented further remodeling of the left ventricle. This method may be useful for treating IMR and improve patients’ prognosis.