A tool and method of positioning and delivering medical devices and therapeutics within the pericardial space, as well as other body part or space. A needle is inserted into the chest through a sub-xiphoid puncture, and the pressure within the needle is monitored manometrically or otherwise sensed as the needle is advanced towards the pericardial space. By reading the pressure within the needle while it is advanced, the clinician is able to know that he or she is avoiding insertion of it into organs or spaces not intended to be the target location. In addition the retractable sharp edge allows the operator to access the space and cut tissue but do so safely by retracting the sharp edge.