Abstract: A process for preserving a patient's organ for transplantation and cardioplegia during cardiac surgery is disclosed which includes harvesting the patient's organ for transplantation or arresting the heart during cardiac surgery, perfusing the organ or heart with an aqueous solution, and removing at least a substantial portion of the aqueous solution from the organ or heart to effect the removal of waste products from the organ before transplantation or restarting the heart. The aqueous solutions of these inventions promote anaerobic glycolysis, remove waste products from the organ and maintain the energy production capacity of the organ and are preferably comprised of about 50 to 150 millimoles of histidine per liter of the solution, at least one energy providing material for maintaining the energy production capacity of the organ, about 60 to 90 millimoles of Na.sup.+ per liter of the solution, about 10 to 25 millimoles of K.sup.