This chapter provides a logical approach to diagnosis of fetal dysrhythmias and discusses the current management of fetal dysrhythmias. Echocardiography, the main diagnostic tool in the fetus, allows recording of the mechanical consequences of the electrical stimulation, registered as myocardial wall movement and blood flow signals. Other techniques such as fetal electrocardiography (f-ECG) or fetal magnetocardiography (f-MCG) allow recording of the electrical cardiac impulses. Rhythm irregularities are common and often associated with premature contraction of the atrium. The most frequent tachycardias are supraventricular tachyarrhythmias including supraventricular tachycardia (SVT) and atrial flutter (AF). Neither heart rate nor fetal heart rate (FHR) variability allows clear distinction among the various types although they may aid diagnosis. Fetal bradycardia may be a manifestation of fetal distress and require emergency Cesarean section. Hydrops increases morbidity and mortality for both tachycardias and bradycardias.