Abstract: A transseptal left atrial cannulation system which provides drainage of left atrial blood without the need for thoracotomy. A guide wire and a long needle assembly are inserted into a catheter. A cannula rides over the exterior of this catheter. The guide wire may be advanced past the needle assembly and through a catheter through the distal end of the catheter to assist in directing the system to the right atrium. The cannulation system is inserted in a femoral vein located in the groin. Both the guide wire and needle assembly are long enough to allow a substantial length to extend out of the body at the groin for manipulation even when the distal ends of the guide wire and needle assembly are positioned in the heart. When the catheter distal end is positioned adjacent the septum in the right atrium, the guide wire is withdrawn from the catheter orifice and the needle assembly moves past the guide wire and through the catheter orifice to a position adjacent to the septum.