Fetal arrhythmia is a term that refers to any abnormality in the fetal heart rate. They are detected in at least 2% of unselected pregnancies during the routine obstetric ultrasound and are normally a temporary, benign occurrence. However, on rare occasions, an irregu-lar heart rhythm can be a significant cause of fetal nonimmune hydrops, premature deli-very, and perinatal morbidity and mortality. Therefore, sustained fetal arrhythmias should be considered an emergency in fetal cardiology and treatment should be promptly institu-ted.