A 72-year-old female presented with congestive heart failure. Ultrasound cardiogram revealed billowing mitral leaflets and severe mitral regurgitation. We diagnosed her with Barlow's disease and performed mitral valve repair. The posterior leaflet was large, and the leaflet height was more than 26 mm. Leaflet height reduction was necessary in order to prevent systolic anterior movement (SAM). The middle scallop was resected in a" W" shape, and its center vertex was designed to have a height of 18 mm, which was the final height of the posterior leaflet. SAM and major leaks were not seen by transesophageal echocardiography after weaning the patient from cardiopulmonary bypass. The use of a W-shaped resection is a simple technique that can be used to reduce the volume and height of the posterior mitral leaflet.