Apparatus comprises: (A) a housing (248), percutaneously deliverable to a heart of a subject, slidable along a guidewire (242), and shaped to define at least one opening (249)； (B) a guide member (250), percutaneously deliverable to the heart, percutaneously removable from the subject, couplable to the housing, and having: (i) a distal portion, comprising a chord-engaging element (252), configured to be percutaneously slidably coupled to and decouplable from at least one chordae tendineae (244), and (ii) a proximal portion, comprising a longitudinal element (251)； and (C) a deployment tool, configured (i) to be reversibly coupled to a tissue anchor (50,280), (ii) to be slidably coupled to the longitudinal element of the guide member, and (iii) to anchor the tissue anchor to a papillary muscle (254) of the subject. Other embodiments are also described.
