Early echocardiographic studies of 50 patients with Shone's complex were retrospectively examined to identify left-sided cardiac features associated with progressive mitral valve (MV) disease requiring intervention, as well as mortality. Thickened MV leaflets, shortened MV chordae coupled with either thickened MV leaflets or turbulence at or below the MV noted by color Doppler, left ventricular outflow tract obstruction without coarctation of the aorta, and mild or moderate aortic insufficiency were associated with a poor prognosis.