A deflecting and sizing apparatus for a catheter handle comprising a catheter shaft having a deflectable distal end portion including a loop member, the apparatus comprising a deflection mechanism configured to be positioned inside the handle and including a pull wire (32, 34) for deflecting the distal end deflectable portion of the catheter shaft, and a loop member adjustment mechanism (108; 200; 308; 408; 508; 608; 708) for adjusting a diameter of the loop member, the loop member adjustment mechanism comprising a loop member pull wire, wherein a distal end of the loop member pull wire is attached to the loop member, a sliding member (128; 228; 328; 404; 504; 604; 704), located within the handle, wherein the sliding member (128; 228; 328) is configured to translate within the handle, and wherein a proximal end of the loop member pull wire is attached to the sliding member (128; 228; 328; 404; 504; 604; 704), a rotatable knob (124; 324; 424; 524; 624; 724) configured to be rotatably coupled to the handle, and an inner actuator (126; 326; 426; 526; 626; 726) positioned between the knob (124; 324; 424; 524; 624; 724) and the sliding member (128; 228; 328; 404; 504; 604; 704), the inner actuator configured to convert rotational movement of the knob (124; 324; 424; 524; 624; 724) to linear movement to translate the sliding member (128; 228; 328; 404; 504; 604; 704) within the handle. a deflection mechanism configured to be positioned inside the handle and including a pull wire (32, 34) for deflecting the distal end deflectable portion of the catheter shaft, and a loop member adjustment mechanism (108; 200; 308; 408; 508; 608; 708) for adjusting a diameter of the loop member, the loop member adjustment mechanism comprising a loop member pull wire, wherein a distal end of the loop member pull wire is attached to the loop member, a sliding member (128; 228; 328; 404; 504; 604; 704), located within the handle, wherein the sliding member (128; 228; 328) is configured to translate within the handle, and wherein a proximal end of the loop member pull wire is attached to the sliding member (128; 228; 328; 404; 504; 604; 704), a rotatable knob (124; 324; 424; 524; 624; 724) configured to be rotatably coupled to the handle, and an inner actuator (126; 326; 426; 526; 626; 726) positioned between the knob (124; 324; 424; 524; 624; 724) and the sliding member (128; 228; 328; 404; 504; 604; 704), the inner actuator configured to convert rotational movement of the knob (124; 324; 424; 524; 624; 724) to linear movement to translate the sliding member (128; 228; 328; 404; 504; 604; 704) within the handle. a loop member pull wire, wherein a distal end of the loop member pull wire is attached to the loop member, a sliding member (128; 228; 328; 404; 504; 604; 704), located within the handle, wherein the sliding member (128; 228; 328) is configured to translate within the handle, and wherein a proximal end of the loop member pull wire is attached to the sliding member (128; 228; 328; 404; 504; 604; 704), a rotatable knob (124; 324; 424; 524; 624; 724) configured to be rotatably coupled to the handle, and an inner actuator (126; 326; 426; 526; 626; 726) positioned between the knob (124; 324; 424; 524; 624; 724) and the sliding member (128; 228; 328; 404; 504; 604; 704), the inner actuator configured to convert rotational movement of the knob (124; 324; 424; 524; 624; 724) to linear movement to translate the sliding member (128; 228; 328; 404; 504; 604; 704) within the handle.