A new clinical entity is described in which free aortic regurgitation from congenital aortic valve disease caused rupture of the chordae to the anterior leaflet of the mitral valve in 7 men aged 45 to 63 years (mean 52 years); 2 of the patients also had rupture of chordae to the posterior leaflet. Comparing these patients with those with ruptured mitral chordae in association with rheumatic heart disease and patients with spontaneous chordal rupture, differences were evident. No patient had a history of rheumatic fever and none had active infection. The typical clinical presentation was of acute mitral regurgitation into a small left atrium, with severe pulmonary oedema which was often resistant to medical treatment. The cause of chordal rupture in these patients was in part the result of progressive left ventricular dilatation, of direct trauma to the anterior cusp of the mitral valve, and possibly of a genetic factor. The anatomical features of both aortic and mitral valves are described, and in 3 histology of the mitral valve was available; 2 had myxomatous degeneration similar to that seen in patients with spontaneous chordal rupture, and in 1 there was degeneration of collagen tissue. All patients were treated surgically but the mortality was high (5 out of 7,70%). Early operation with replacement of the aortic and mitral valves is recommended if this high mortality is to be reduced.