Cardiopulmonary bypass makes a mess of homeostasis. Extracorporeal perfusion produces pulseless flow without physiologic controls, showers microemboli throughout the body, and brings blood diluted with additives to an enzymatic boil. Much of the morbidity associated with open heart surgery is due to contact of blood with the synthetic surfaces of the extracorporeal perfusion circuit. Bypass temporarily impairs function of every organ, alters concentrations of over 25 vasoactive substances within the plasma, and causes massive retention of fluid. In short, cardiopulmonary bypass makes patients sick.