Congenital ostial membrane of left main coronary artery.

Abnormalities of coronary artery development, origin, and distribution are being diagnosed and treated successfully with increasing frequency. This report describes the case histories of two patients with stenosis of the left main coronary artery caused by a congenital ostial membrane; both patients were successfully treated by operation. A similar abnormality has been reported only once in the literature, having been discovered at autopsy.