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 closest to the cardiac interatrial septum of a patient when the transseptal insertion device is in use and a proximal end that is external to the patent; a balloon that is connected to the distal end of the sheath , wherein: the balloon , when inflated and the transseptal insertion device is in use, overhangs and extends 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 a dilator that is positioned within the at least one lumen when the transseptal insertion device is in use, wherein the dilator has a distal end and is designed to and is capable of precisely puncturing the cardiac interatrial septum , characterised in that the balloon includes one or more ultrasound transceivers that emit and receive ultrasound waves, convert the ultrasound waves to electrical signals, and transmit the electrical signals to an external imaging device that produces images of the cardiac interatrial septum from the received signals, wherein the one or more ultrasound transceivers are located on the balloon surface, wherein the one or more ultrasound transceivers are oriented towards the cardiac interatrial septum when the balloon is fully inflated and the distal end of the sheath is oriented towards the cardiac interatrial septum . a sheath that defines at least one lumen therein and has a distal end that is closest to the cardiac interatrial septum of a patient when the transseptal insertion device is in use and a proximal end that is external to the patent; a balloon that is connected to the distal end of the sheath , wherein: the balloon , when inflated and the transseptal insertion device is in use, overhangs and extends 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 a dilator that is positioned within the at least one lumen when the transseptal insertion device is in use, wherein the dilator has a distal end and is designed to and is capable of precisely puncturing the cardiac interatrial septum , characterised in that the balloon includes one or more ultrasound transceivers that emit and receive ultrasound waves, convert the ultrasound waves to electrical signals, and transmit the electrical signals to an external imaging device that produces images of the cardiac interatrial septum from the received signals, the balloon , when inflated and the transseptal insertion device is in use, overhangs and extends 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 a dilator that is positioned within the at least one lumen when the transseptal insertion device is in use, wherein the dilator has a distal end and is designed to and is capable of precisely puncturing the cardiac interatrial septum , characterised in that the balloon includes one or more ultrasound transceivers that emit and receive ultrasound waves, convert the ultrasound waves to electrical signals, and transmit the electrical signals to an external imaging device that produces images of the cardiac interatrial septum from the received signals, wherein the one or more ultrasound transceivers are located on the balloon surface, wherein the one or more ultrasound transceivers are oriented towards the cardiac interatrial septum when the balloon is fully inflated and the distal end of the sheath is oriented towards the cardiac interatrial septum . <EOS>