A double guidewire comprising: (a) a first guidewire comprising an elongated flexible shaft and having a distal portion that terminates in a distal tip, said distal portion of said first guidewire comprising a deflectable helical coil (112, 113), said first guidewire being a hollow guidewire having a central lumen extending along a length of said first guidewire; (b) a second guidewire comprising an elongated flexible shaft and having a distal portion that terminates in a distal tip, said distal portion of said second guidewire comprising a deflectable helical coil, said second guidewire being deployed within said central lumen of said first guidewire; and (c) an adjuster mechanism mechanically linked to a proximal portion of at least said second guidewire, said adjuster mechanism being operable to displace said second guidewire longitudinally relative to said first guidewire between: (i) a first state in which said distal tip of said second guidewire is adjacent to said distal tip of said first guidewire, (ii) a second state in which at least part of said distal portion of said second guidewire is advanced beyond said distal tip of said first guidewire, and (iii) a third state in which said distal tip of said second guidewire is withdrawn proximally along said central lumen so as to leave empty a part of said central lumen along at least part of said distal portion of said first guidewire; wherein a region of said distal portion adjacent to said distal tip of each of said first and second guidewires is configured to be inelastically deformable or preshaped to impart a lateral deflection to said distal portion, said region of said distal portion adjacent to said distal tip of said first guidewire having a first length, and wherein, when said region of said distal portion adjacent to said distal tip of each of said first and second guidewires is deflected, withdrawal of said second guidewire proximally along said central lumen, from said first state to said third state, such that the deflected regions of said first and second guidewires are longitudinally displaced relative to each other, causes a second length of a distal portion of the double guidewire to be deflected, said second length being longer than said first length. (a) a first guidewire comprising an elongated flexible shaft and having a distal portion that terminates in a distal tip, said distal portion of said first guidewire comprising a deflectable helical coil (112, 113), said first guidewire being a hollow guidewire having a central lumen extending along a length of said first guidewire; (b) a second guidewire comprising an elongated flexible shaft and having a distal portion that terminates in a distal tip, said distal portion of said second guidewire comprising a deflectable helical coil, said second guidewire being deployed within said central lumen of said first guidewire; and (c) an adjuster mechanism mechanically linked to a proximal portion of at least said second guidewire, said adjuster mechanism being operable to displace said second guidewire longitudinally relative to said first guidewire between: (i) a first state in which said distal tip of said second guidewire is adjacent to said distal tip of said first guidewire, (ii) a second state in which at least part of said distal portion of said second guidewire is advanced beyond said distal tip of said first guidewire, and (iii) a third state in which said distal tip of said second guidewire is withdrawn proximally along said central lumen so as to leave empty a part of said central lumen along at least part of said distal portion of said first guidewire; (i) a first state in which said distal tip of said second guidewire is adjacent to said distal tip of said first guidewire, (ii) a second state in which at least part of said distal portion of said second guidewire is advanced beyond said distal tip of said first guidewire, and (iii) a third state in which said distal tip of said second guidewire is withdrawn proximally along said central lumen so as to leave empty a part of said central lumen along at least part of said distal portion of said first guidewire;