Devices for securing prostheses such as heart valves or annuloplasty rings with sutures and without using knots are disclosed. The devices are particularly well suited for traditional surgery or minimally invasive surgery, and improve the ease of implantation by eliminating surgical knots a clinician would normally tie in the limited space in and around the implant site. The devices have opposed the clamp halves surrounded by a coil spring. Sutures pass between the clamp halves and the coil spring has an inner coil diameter sufficient to compress the sutures between the clamp. A retention member positioned between the clamp halves maintains a minimum space and therebetween to enable the locking device to be slid along the sutures into position, and to adjust the tension of the sutures therethrough. A delivery tool may be used to deliver and deploy the locking devices.