Mitral valve "anular" calcium forming a complete circle or "O" configuration: clinical and necropsy observations.

Attention is called to the occurrence of a complete circle or "O"-shaped ring of calcium at the mitral anular region in each of two women, aged 67 and 82 years. Extension of mitral anular calcium from behind the posterior mitral leaflet across the ventricular aspect of the anterior mitral leaflet to form a complete circle has not been reported previously.