Needleless access port valves are generally discussed herein with particular discussions extended to needleless access port valves incorporating a piston comprising slit along an upper piston section for accommodating fluid flow. The slit opens when the piston is compressed by a medical implement, such as a syringe tip, to permit fluid communication between the inlet and the outlet of the vale housing. The slit may be cut using high frequency cutting machine or a multi-axis robot arm and a cutting blade.