A device for reshaping a mitral valve annulus (25), said device being elongate and having such dimensions as to be insertable into a coronary sinus (24). The device comprises fixing means (22, 23; 22a, 23a) for fixing the ends of the device within the coronary sinus (24); anda shape changing member (20a; 7; 7a; 9) extending between the fixing means (22, 23; 22a, 23a). The shape changing member (20a; 7; 7a; 9) includes a plurality of adjacent structural cells. The device includes resorbable delay means (21 a; 8; 8a; 10) that in a first configuration retrains at least two of said plurality of adjacent structural elements in a first, relatively elongate state of shape (K; D; E) and wherein the delay means in a second configuration releases said at least two adjacent structural elements to assume a second, relatively shortened state of shape (K'; D'; E'), thereby reducing a length of the shape-changing member (20a; 7; 7a; 9). The delay means (21 a; 8; 8a; 10) moves from its first configuration to its second configuration upon resorbtion of the delay means.