A sizing tool for use in implanting a composite valved conduit having a prosthetic heart valve on a distal end attached to a conduit graft that extends to a proximal end. The tool includes a proximal handle and a distal shaft, a prosthetic heart valve sizer having an axis affixed to a distal end of the shaft, and a conduit graft replica having an axis mounted on the shaft proximal to the heart valve sizer. A method of securing a composite valved conduit includes introducing to an excised ascending aorta the sizing tool, measuring the aortic annulus with the prosthetic heart valve sizer, and determining whether the coronary arteries have sufficient length or whether an additional tubular coronary extension segment is required to add to one or both of the ends of the coronary arteries by extending the coronary arteries toward the conduit graft replica.