Abstract. Fetal arrhythmias occur commonly, but most are benign. Clinically signiﬁcant arrhythmias should be distinguished and managed. Supraventricular tachycardia (SVT) and severe bradycardia from complete heart block (CHB) can progress to heart failure and hydrops fetalis. This retrospective review of 2042 fetal echocardiograms aims to characterize an institutional experience with fetal arrhythmias. 131 fetuses were referred for arrhythmia evaluation. Premature atrial contractions (PACs) were found in 67 (51%) of which a third had a prominent atrial septal aneurysm. 49 (37%) had sinus rhythm (no noted arrhythmia). 15 (11%) had hemodynamically signiﬁcant arrhythmias, which included fetal tachycardias in 12 (9%) and CHB in 3 (2%). All fetuses with tachycardia had structurally normal hearts. 10 had fetal SVT (3 with hydrops and 7 without hydrops) and 2 had atrial ﬂutter (1 with hydrops and 1 without hydrops). All fetuses in tachycardia were converted to sinus rhythm and 2 required antiarrhythmic treatment after birth. CHB was found in 3 fetuses. Major cardiac malformations and hydrops were noted in 2 of these fetuses, both resulting in fetal demise. The third fetus with CHB had a structurally normal heart, was associated with maternal systemic lupus erythematosus (positive SS-A, SS-B antibodies), and required a pacemaker after birth. PACs and sinus rhythm were the most common diagnosis in fetuses referred for arrhythmia evaluation. Despite the presence of hydrops, SVTs responded well to maternal administration of antiarrhythmic therapy and were successfully converted to sinus rhythm. CHB can be associated with maternal autoimmune disease and certain cardiac malformations. The prognosis of CHB in the presence of cardiac disease is poor.