A tool for coring a hole in a portion of a patient's body. A cylindrical sheath includes a hollow bore open at both ends. A shaft is axially movable back and forth within the bore. A blade assembly is attached to one end of the shaft. The blade assembly comprises a hollow open cup portion having a closed end and a cutting edge formed around the margin of the open end. An interface is attached to the sheath which is shaped and dimensioned to communicate with a connector used to connect a medical device to a patient's body.