Atrial septal defect transcatheter occlusion techniques have become a reliable alternative to surgical procedures. Possible complications can derive from unfavorable anatomy of the defect and over-dimensioning of the device. We describe the first case ever reported of anterior mitral leaflet perforation caused by an atrial septal occluder. The diagnosis was performed by conventional echocardiography and 3 dimensions helped for a more accurate anatomic definition. Device removal, atrial septal defect closure, and repair of the mitral tear were then successfully performed.