Implantable tissue structure modification devices are provided. Aspects of the tissue structure modification devices include first and second tissue securers separated by a contraction region, wherein the device is configured to be implanted at a cardiac location and assume a first constrained length that is longer than a second relaxed length. Also provided are methods of using the devices for tissue structure modification, as well as delivery systems and kits that find use in the methods. The devices and methods of the invention find use in a variety of different applications, including valve (e.g., mitral valve) structure modification.