Mitral valve in secundum atrial septal defects.

The mitral valve in 15 of 16 adult hearts with unclosed secundum atrial septal defects showed a consistent abnormality consisting of thickening of the medial half of the anterior cusp and some fusion of adjacent chordae. Histologically the lesion is a surface fibrosis without vascularisation or myxomatous change to suggest a rheumatic or floppy valve. The high frequency and morphological appearances suggest abnormal cusp movement and resultant valve trauma rather than a primary valve abnormality. The functional abnormality leading to secondary valve changes is presumably related to increased flow and altered left ventricular geometry but cannot be studied in the dead heart.