A single fold system for tissue approximation and fixation is described herein. The devices are advanced in a minimally invasive manner within a patient's body to create at least one fold within a hollow body organ. The system comprises a tissue acquisition and folding device and a tissue stapling or fixation device, each of which is used together as a system. The acquisition device is used to approximate a single fold of tissue from within the hollow body organ and the stapling device is advanced through a main lumen defined through the acquisition device and is used to affix the tissue. The stapling device is keyed to maintain its rotational orientation relative to the acquisition device and to provide the user positional information of the stapling device. The acquisition device is also configured to provide lateral stability to the stapling device prior to the stapling device being clamped onto tissue.