A method for use with a heart of a subject includes advancing a tool distally along a flexible elongate contracting member, toward an anchor implanted at the heart. Tension is applied to the contracting member such that the contracting member slides proximally through a fastener disposed at the heart while a stop coupled to the fastener maintains the fastener in an open state. Using the tool, the stop is pulled proximally (i) away from the fastener, such that the fastener responsively clamps to the contracting member, thereby locking the tension in the contracting member, and (ii) against a cutting element of the tool such that the cutting element moves in a manner that severs the contracting member. Other embodiments are also described.