Mares give birth under high parasympathetic tone as indicated by increased heart rate variability (HRV) and atrioventricular blocks. These changes might be induced by oxytocin released at foaling. In this short communication, the cardiac (n = 4) and cortisol response (n = 3) of mares treated with oxytocin infusions because of fetal membrane retention are reported. A marked cortisol release occurred during oxytocin infusion in two mares but not in a third mare which was infused for 6 minutes only. Oxytocin-induced cortisol release was neither accompanied by an increase in heart rate nor a decrease in HRV, and heart rate even decreased during oxytocin infusions. Preliminary data indicate that cortisol release in oxytocin-treated mares is not a stress response. Treatment of retained membranes in mares with oxytocin does not induce cardiovascular side effects.