In laboratory investigations, vasopressin given during CPR resulted in improved vital organ blood flow when compared with epinephrine. Given the profound and long lasting vasopressor effects of vasopressin, we tested the hypothesis that vasopressin given during CPR would result in renal and splanchnic hypoperfusion in the post-resuscitation period when compared with epinephrine. After 4 min of ventricular fibrillation, 16 pigs were randomly assigned to receive either 0.045 mg x kg(-1) epinephrine or 0.4 U X kg(-1) vasopressin before defibrillation. Splanchnic and renal blood flow were measured 30, 90, and 240 min after restoration of spontaneous circulation (ROSC) in the epinephrine and vasopressin groups and in a control group of eight pigs using radiolabeled microspheres. Hepatic blood flow was measured before arrest and 30, 90, and 240 min after ROSC by means of indocyanine green infusion. Thirty minutes after ROSC, renal and adrenal blood flow were significantly lower in the vasopressin group (300 [273-334] and 256 [170-284] ml X min(-1) x 100 g(-1)) (median and 25th and 75th percentile) as compared with the epinephrine group (370 [346-429] and 360 [326-420] ml x min(-1) x 100 g(-1); P < 0.05). Pancreatic, intestinal, and hepatic blood flow were not significantly different in animals after receiving epinephrine or vasopressin. In comparison to epinephrine, vasopressin given during cardiac arrest impairs renal and adrenal perfusion temporarily but does not lead to intestinal or hepatic hypoperfusion in the post-resuscitation phase.