Seven human fetuses with intermittently recurring cardiac arrhythmias of ectopic origin were studied intensively during labor and the early neonatal period. Neonatal outcome, judged by Apgar scores and neonatal acid-base parameters, was favorable in all 7 patients. Three of the seven arrhythmias reverted spontaneously to sinus rhythm within 72 hours, and six of the seven resolved by 5 days of age. One neonate, with supraventricular tachycardia, developed congestive heart failure, necessitating digitalization, but was free of symptoms at 6 weeks and showed no evidence of congenital heart disease. The literature on fetal cardiac arrhythmias is reviewed. A number of etiologic mechanisms and several methods of pharmacologic therapy of these irregularities have been proposed. These cases suggest, however, that fetal arrhythmias of ectopic origin need not represent signs of fetal distress or cardiac anomaly and may be inocuous. Evidence to date indicates that in utero pharmacologic treatment of fetal arrhythmias is not indicated.