An expansion and locking mechanism for a prosthetic valve and associated methods are disclosed. As one example, an expansion and locking mechanism for an implantable prosthetic device can include a first member coupled to a frame of the device and including at least one extension member extending in a circumferential direction and having a free end biased radially inward, into an interior of the first member and a second member coupled to the frame at a second location spaced apart from the first location, the second member extending at least partially inside the first member and comprising a plurality of radial extensions spaced apart from one another along a portion of a length of the second member, the plurality of radial extensions arranged in a first side of the second member that is arranged opposite a second side of the second member, the second side not including any radial extensions.