In 13 patients, episodes of transient fetal cardiac arrest were observed in a group of 594 extensively monitored labors during a given 3-year period. The number of episodes per patient ranged from one to six, with a maximal duration of cardiac arrest (R-R interval) being 5.2 seconds. All of the patients responded to changing maternal position or termination of pregnancy except 1. This patient received Atropine as a premedication for cesarean section. The parasympatholytic properties of Atropine minimized the severity of cardiac arrest. The effect of cardiac arrest on fetuses is not clearly shown in these preliminary observations. The prompt elimination of cardiac arrest is thought to be imperative in reducing perinatal loss. Cardiac arrest is thought to be an extensive form of severe variable deceleration. The hypothesis is made that these fetuses had an unbalanced autonomic nervous system and/or an overwhelming vagal tone. If these signs are detected early by fetal monitoring, attention should be paid to the possibility of cardiac arrest.