Fetal, maternal and newborn electrocardiograms were studied on a seven-year-old mare during the entire course of normal parturition. A summary of the results is as follows : 1) The fetal heart rate indicated 60〜66 beats per minute before the onset of parturition, and it declined a little with the commencement of the first stage of labor, keeping a level of 54〜60 until the fetus was expelled. The heart rate of the newborn foal increased rapidly, ranging 108〜216. These values of the newborn corresponded to about 2〜4 times those before expulsion. 2) Throughout the whole course of parturition, the maternal heart rate was generally stable with a range of 48〜60,but arrhythmia was sometimes observed especially at later stages of parturition. This arrhythmia was characterized by incomplete A-V block. 3) After when the fetal head was exposed, fetal Q-Q intervals become highly irregular. 4) Characteristic changes of the pattern of fetal QRS were recognized at respective labor stages during parturition : Rs type before the onset of labor pains, types of qRS, Rs and QR from the commencement of the first stage of labor to 2 minutes before rupture of the amniotic sac, and Qr type immediately before the rupture. Relationships between these types of fetal QRS and fetal positions in the uterus were also discussed from the viewpoint of obstetrical use of ECG during parturition of the horse
