Apparatus comprising: a plurality of tissue anchors, which are shaped so as to define respective channels along entire longitudinal lengths of the anchors, and each of which has a central longitudinal axis and comprises: a helical tissue coupling element, having proximal and distal ends; and a tool-engaging head, fixed to the proximal end of the helical tissue coupling element, which tool-engaging head is shaped so as to define a non-circular engaging opening that passes entirely through the tool-engaging head along the axis, wherein the helical tissue coupling element and the tool-engaging head together define the channel of the tissue anchor along an entire length of the tissue anchor and wherein the channel of each of the anchors is sized and shaped such that a right circular cylinder could be placed within the channel, coaxial with the tissue anchor, and along the entire length of the tissue anchor; and an anchor deployment tool, which comprises: a flexible outer tube, which has a distal tube end; a flexible inner shaft, which is positioned within the flexible outer tube, and has a distal shaft end; and a rotating deployment element, which is coupled to the distal shaft end, wherein the anchor deployment tool is configured to provide an anchor storage area having a distal anchor storage area end wherein a distance between the distal anchor storage area end and the distal tube end is at least 3 cm, in which anchor storage area the plurality of tissue anchors are initially stored, such that the flexible inner shaft passes through the channels of the anchors, and the anchors are within the flexible outer tube, wherein the rotating deployment element is configured to directly engage the anchors in the anchor storage area one at a time, by removably engaging the tool-engaging head of each of the anchors; advance each of the anchors, while thus directly engaged, in a distal direction; and deploy each of the anchors through the distal tube end and into tissue of a subject, wherein the anchor deployment tool is configured such that only the single anchor being advanced at the time by the rotating deployment element is within a distal anchor manipulation area of the anchor deployment tool between the distal anchor storage area end and the distal tube end. a plurality of tissue anchors, which are shaped so as to define respective channels along entire longitudinal lengths of the anchors, and each of which has a central longitudinal axis and comprises: a helical tissue coupling element, having proximal and distal ends; and a tool-engaging head, fixed to the proximal end of the helical tissue coupling element, which tool-engaging head is shaped so as to define a non-circular engaging opening that passes entirely through the tool-engaging head along the axis, wherein the helical tissue coupling element and the tool-engaging head together define the channel of the tissue anchor along an entire length of the tissue anchor and wherein the channel of each of the anchors is sized and shaped such that a right circular cylinder could be placed within the channel, coaxial with the tissue anchor, and along the entire length of the tissue anchor; and a helical tissue coupling element, having proximal and distal ends; and a tool-engaging head, fixed to the proximal end of the helical tissue coupling element, which tool-engaging head is shaped so as to define a non-circular engaging opening that passes entirely through the tool-engaging head along the axis, wherein the helical tissue coupling element and the tool-engaging head together define the channel of the tissue anchor along an entire length of the tissue anchor and wherein the channel of each of the anchors is sized and shaped such that a right circular cylinder could be placed within the channel, coaxial with the tissue anchor, and along the entire length of the tissue anchor; and an anchor deployment tool, which comprises: a flexible outer tube, which has a distal tube end; a flexible inner shaft, which is positioned within the flexible outer tube, and has a distal shaft end; and a rotating deployment element, which is coupled to the distal shaft end, a flexible outer tube, which has a distal tube end; a flexible inner shaft, which is positioned within the flexible outer tube, and has a distal shaft end; and a rotating deployment element, which is coupled to the distal shaft end,