A 16-year-old male with a history of surgically-closed atrial septal defect (ASD) 2 years before was admitted to our hospital for lung congestion caused by severe mitral regurgitation (MR). Before the closure of the ASD, his echocardiographic findings showed mild prolapse of the anterior mitral leaflet (AML) with the hypoplastic posterior mitral leaflet (PML), but only mild MR. On admission, severe MR was observed by echocardiography in association with an increase in mitral anural size and the progression of AML prolapse. It was assumed that the worsening of MR was due to increased blood volume in the left-side of the heart after closing the ASD combined with cardiac growth. After mitral valvuloplasty, MR and heart failure disappeared.
