The present invention relates to organ perfusion systems that can be used at room temperature. The organ perfusion systems do not comprise a temperature controller. In some embodiments, the organ perfusion systems do not comprise a cleaning device for cleaning the perfusion fluid. The perfusion fluid can comprise Williams' medium E. The organ perfusion systems can be portable and can be used to preserving an organ, preventing ischemic damage in an organ, or recovering an ischemically damaged organ.