A transseptal insertion device which is suitable for facilitating precise and safe transseptal puncture of a cardiac interatrial septum , comprising: a sheath that defines at least one lumen therein and has a distal end that is positioned toward the cardiac interatrial septum of a patient when the transseptal insertion device is in use and a proximal end that is external to the patient; one or more positioning balloons that are connected to the distal end of the sheath , wherein the one or more positioning balloons, when inflated and the transseptal insertion device is in use, overhang and extend past the distal end of the sheath, preventing accidental puncturing of the cardiac interatrial septum and stabilizing the transseptal insertion device against fossa ovalis of the cardiac interatrial septum, and wherein the sheath includes one or more deflation ports to deflate the one or more positioning balloons ; a puncture member movably positioned within the at least one lumen , wherein the puncture member has a distal end that is positioned toward the cardiac interatrial septum of the patient; and a puncture member balloon located on the puncture member , wherein the puncture member balloon, when inflated, is capable of sealing the one or more deflation ports of the sheath , permitting the inflation of the one or more positioning balloons , wherein the puncture member balloon is aligned with the one or more deflation ports of the sheath while the puncture member balloon stays inside the sheath , and wherein the puncture member balloon is configured to move away from the one or more deflation ports of the sheath when the puncture member moves past the distal end of the sheath . a sheath that defines at least one lumen therein and has a distal end that is positioned toward the cardiac interatrial septum of a patient when the transseptal insertion device is in use and a proximal end that is external to the patient; one or more positioning balloons that are connected to the distal end of the sheath , wherein the one or more positioning balloons, when inflated and the transseptal insertion device is in use, overhang and extend past the distal end of the sheath, preventing accidental puncturing of the cardiac interatrial septum and stabilizing the transseptal insertion device against fossa ovalis of the cardiac interatrial septum, and wherein the sheath includes one or more deflation ports to deflate the one or more positioning balloons ; a puncture member movably positioned within the at least one lumen , wherein the puncture member has a distal end that is positioned toward the cardiac interatrial septum of the patient; and a puncture member balloon located on the puncture member , wherein the puncture member balloon, when inflated, is capable of sealing the one or more deflation ports of the sheath , permitting the inflation of the one or more positioning balloons , wherein the puncture member balloon is aligned with the one or more deflation ports of the sheath while the puncture member balloon stays inside the sheath , and wherein the puncture member balloon is configured to move away from the one or more deflation ports of the sheath when the puncture member moves past the distal end of the sheath . <EOS>