The aim of this study was to investigate the effects of maternal exercise on fetal movement and heart rate patterns. Twelve healthy women at 29-32 weeks of pregnancy performed a (sub)maximal bicycle exercise test, reaching 53-99% (median 82%) of their maximal increase in heart rate (MIHR). Fetal heart rate (FHR) and its variation and fetal body and breathing movements were recorded for 1 h before and after the exercise and also on a control day. After exercise, FHR was higher for 30 min and FHR variation reduced for 20 min as compared with pre-exercise levels (P < 0.01). Fetal body movements were reduced for the first 5 min following exercise (P < 0.05). In two cases, fetal bradycardia was observed (at 89 and 99% MIHR) followed by a considerable reduction in FHR variation and absence of body and breathing movements for 20 min. In the other 10 fetuses fetal breathing activity was increased for the first 5 min after exercise (P < 0.05). FHR (and to a lesser extent breathing movements) increased with increasing level of maternal exercise, but decreased when the % MIHR exceeded approximately 90%. Body movements were negatively correlated with the % MIHR (P < 0.05). In conclusion, moderate to heavy maternal exercise clearly affects the human fetus with signs of transient fetal impairment after heavy exercise.