Five cows in the last month of gestation, provided with uterine electrodes and in which catheters had been chronically installed in the fetal aorta, were used to study patterns of fetal heart rate (FHR) and the influence of periods of myometrial electrical activity during gestation (contractures) on FHR. The FHR was calculated by counting the number of blood pressure pulses on the tracings during alternate periods of 12 seconds. Three 1-hour recordings without contractures and 10 recordings during the time of a contracture were randomly selected for each cow. The calculated data points were plotted on a graph to display FHR patterns. In 41 periods associated with single contractures, FHR data points were taken every 72 seconds. Changes in absolute and relative FHR in these periods were determined to analyze a possible effect of contractures on FHR. Three types of variation in FHR patterns could be distinguished: a short-term, low-amplitude variation of basal FHR; a second type in which the duration was < 4 minutes and the amplitude was > or = 15 beats/min; and prolonged periods with increased or decreased FHR values (> 4 minutes and > or = 15 beats/min). The relationship between these types of variation and fetal activity states remains to be established for cows. During the 60 hours of recordings that were analyzed, a period of several minutes during which FHR values were extremely high (> 180 beats/min) was found 3 times. There were no significant differences in absolute or relative FHR before, during, or after a contracture.