A dynamic, adjustable annuloplasty ring sizer can include an adjustable ring replica, which can be adjusted through a range of sizes corresponding to available prosthetic annuloplasty repair ring sizes. Actuation of an adjustment trigger on a handle portion of the ring sizer can displace tension wires that extend through a malleable shaft and through a plurality of articulating segments that form the ring replica. Displacement of the tension wires causes flexion of the joints between adjacent articulating segments, thereby reducing the overall size of the ring replica. Releasing the tension wires can allow an elastic extension wire to act on the ring replica, enlarging the ring replica to its maximum, at-rest size. In this manner, the appropriate size of annuloplasty ring prosthesis can be determined with a single device, without requiring a plurality of static ring sizers that require individual insertion and placement for the conventional trial-and-error sizing methods.