(1) [TA], a large oval opening in the base of the greater wing of sphenoid bone, transmitting the mandibular division of the trigeminal nerve and a small meningeal artery; (2) valvular incompetence of the oval foramen of the heart; a condition contrasting with probe patency of the oval foramen in that the oval foramen valve has abnormal perforations in it, or is of insufficient size to afford adequate valvular action at the foramen ovale prenatally, or effect a complete closure postnatally. SYN: foramen ovale of heart, foramen ovale.