An endovascular surgical tool includes a flexible, electrically-conductive corewire, a return conductor, a resistive heating element attached to the distal end of the corewire, and a therapeutic payload attached to the loop of the resistive heating element by a coil connecting member. The corewire includes at least one segment at its distal end which transitions from the substantially uniform cross-section of its proximal end to a smaller distal cross-section. The return conductor is electrically insulated from and bonded to the corewire. The resistive heating element includes a first terminal electrically connected to the corewire, a second terminal electrically connected to the return conductor, a helical coil, and a loop. The helical coil and the loop are electrically in series between the first terminal and the second terminal. The coil connecting member has a release temperature lower than a loop melting temperature of the loop of the resistive heating element.
