An organ perfusion apparatus and method monitor, sustain and/or restore viability of organs and preserve organs for storage and/or transport. Other apparatus include an organ transporter, an organ cassette and an organ diagnostic device. Organ viability is restored by restoring high energy nucleotide (e.g., ATP) levels by perfusing the organ with a medical fluid, such as an oxygenated cross-linked hemoglobin-based bicarbonate medical fluid, at normothermic temperatures. In the hypothermic mode, the organ is perfused with a medical fluid, preferably a simple crystalloid solution containing antioxidants, intermittently or in slow continuous flow. Viability of the organ may be automatically monitored, preferably by monitoring characteristics of the medical fluid perfusate. The perfusion process can be automatically controlled using a control program.