A system for use with a subject, the system comprising: a tether configured to be transluminally advanced into a coronary blood vessel of the heart of the subject, the coronary blood vessel at least partially transcribing a heart chamber of the heart, the tether having a first terminus and a second terminus , the first terminus configured to be advanced through a wall of the coronary blood vessel into the heart chamber at a first location and the second terminus configured to be advanced through the wall of the coronary blood vessel into the heart chamber at a second location ; at least one device configured to transluminally draw the first and second termini of the tether , from the first and second locations , respectively, out of the heart chamber, such that a first segment of the tether extends from the first location through the heart chamber and a second segment of the tether extends from the second location through the heart chamber; a support tube defining a lumen, the support tube being configured to be transluminally advanced into the coronary blood vessel , the tether extending through the lumen of the support tube and being slidable relative to the support tube ; at least one tissue anchor (50, 56; 80), configured to be slid over and along at least one of the first and second termini , and to anchor the at least one of the first and second termini to tissue of the heart chamber, such that a part of the tether extends between the at least one tissue anchor (50, 56; 80) and the coronary blood vessel ; and at least one lock (60, 66; 70), configured, following tensioning of the tether , to lock tension in the tether . a tether configured to be transluminally advanced into a coronary blood vessel of the heart of the subject, the coronary blood vessel at least partially transcribing a heart chamber of the heart, the tether having a first terminus and a second terminus , the first terminus configured to be advanced through a wall of the coronary blood vessel into the heart chamber at a first location and the second terminus configured to be advanced through the wall of the coronary blood vessel into the heart chamber at a second location ; at least one device configured to transluminally draw the first and second termini of the tether , from the first and second locations , respectively, out of the heart chamber, such that a first segment of the tether extends from the first location through the heart chamber and a second segment of the tether extends from the second location through the heart chamber; a support tube defining a lumen, the support tube being configured to be transluminally advanced into the coronary blood vessel , the tether extending through the lumen of the support tube and being slidable relative to the support tube ; at least one tissue anchor (50, 56; 80), configured to be slid over and along at least one of the first and second termini , and to anchor the at least one of the first and second termini to tissue of the heart chamber, such that a part of the tether extends between the at least one tissue anchor (50, 56; 80) and the coronary blood vessel ; and at least one lock (60, 66; 70), configured, following tensioning of the tether , to lock tension in the tether . <EOS>