The work investigated functional and mechanical properties of the NiTi alloy specimens subjected to various thermal treatments at different temperatures. The stress-strain diagrams were studied at different temperatures. The results showed that a sample of the NiTi alloy wires of Ti - 50.84 at.% Ni alloys with a diameter of 0.5 mm that was annealed at 773 K for 1 hour demonstrated the best functional properties. This specimen showed good recovered strain 6 - 8%, low critical stress 250 - 450. Therefore, it was the best candidate for fabrication of an implantable device for repair of mitral valve prolapse.