Triggering events with GPUs at ATLAS

The growing complexity of events produced in LHC collisions demands more and more computing power both for the online selection and for the offline reconstruction of events. In recent years, the explosive performance growth of massively parallel processors like Graphics Processing Units~(GPU) both in computing power and in low energy consumption, make GPU extremely attractive for using them in a complex high energy experiment like ATLAS. Together with the optimization of reconstruction algorithms this new massively parallel paradigm is exploited. For this purpose a small scale prototype of the full ATLAS High Level Trigger involving GPU has been implemented. We discuss the integration procedure of this prototype, the achieved performance and the prospects for the future