Uterine ischemia results in severe cardiac disturbances in the fetus. It has been postulated that these effects are due to interaction with the ischemic uterus or placenta and not due to hypoxia or build up of metabolites in the fetus. The fetal cardiac responses to uterine clamping and umbilical cord clamping were compared in the rat using electrocardiography (ECG). On day 21 of gestation fetuses from the same pregnant rat were exposed to umbilical clamping, uterine clamping or no clamping in a total of 14 pregnant rats. ECGs were recorded for each fetus immediately after clamping and at 10, 20 and 30 minutes after clamping. Immediately after clamping, the uterine clamping group showed severe sinus bradycardia. At all other observation time fetuses exposed to uterine or umbilical clamping showed bradycardia and other ECG changes typically associated with hypoxia. Therefore, umbilical clamping protected the fetuses from the adverse effects of uterine clamping for only a very short time.