Congenital malformations of the mitral valve (MV) are rare, and the majority are detected in infancy and are associated with significant mortality.1 In particular, descriptions of unileaflet MV (ULMV; either partial or complete leaflet agenesis) are limited to a few case reports.2 We present the case of a 65-year-old woman who presented with exertional dyspnea. She was found on echocardiography to have an elongated anterior MV with complete absence of the posterior mitral leaflet, and she went on to undergo successful MV repair using a novel surgical approach. Imaging findings in this case provide unique insight into the embryologic basis of this abnormality and assisted in planning the surgical approach.