Little is known about the efficacy of CPR in the setting of hypothermia-induced cardiac arrest. We measured organ blood flow produced by conventional closed-chest CPR in eight swine following normothermic KCl-induced cardiac arrest and in seven swine surface-cooled until cardiac arrest occurred. Radiomicrospheres were injected in the unanesthetized basal state, after five minutes of CPR, and after 20 minutes of CPR. After five minutes of CPR, the cardiac output and cerebral and myocardial blood flows (mean +/- SD) of hypothermic animals were 15.3 +/- 7.5 mL/min/kg, 0.16 +/- 0.11 mL/min/g, and 0.20 +/- 0.15 mL/min/g, respectively. Mean percentage flows were 7%, 15%, and 8%, respectively, of those measured in the unanesthetized prearrest state, and 50%, 55%, and 31%, respectively, of the flow produced during CPR in normothermic animals. Blood flow during hypothermic CPR did not change significantly over time; however, during normothermic CPR, cardiac output and cerebral and myocardial flows decreased so that at 20 minutes there were no significant differences from those values measured in hypothermic animals. The reduction in organ flow produced by external chest compression in hypothermic animals may be a result of the changes in the viscoelastic properties of the thorax that occur during profound hypothermia.