The normal fetal cardiac rhythm is characterized by a regular heart rate ranging between 100 and 160 -180 beats/min with a normal 1: 1 atrioventricular electromechanical relationship during each cardiac cycle. Fetal tachycardia occurring in approximately 0.5% of all pregnancies and it is an important cause of fetal morbidity and mortality. A fetal tachycardic heart is at risk for developing low cardiac output, hydrops and ultimately fetal death or significant neurological morbidity. Different conditions can play a role to determine the natural history of tachycardic fetus as gestational age, underlying pathophysiology of the arrhythmia, fetal heart rate, duration of the tachyarrhythmia, and presence or absence of cardiac dysfunction. Reliable diagnosis in utero of fetal arrhythmia is possible by ultrasound examination of the fetal heart. In fact pulsed wave Doppler guided by two-dimensional echocardiography provided important information on cardiac rhythm as it study the blood flow from different chambers. With the introduction of the latest myocardial deformation methodology, the fetal tachyarrhythmias can be diagnosed more accurately. Precise diagnosis of cardiac arrhythmias in the fetus is crucial for a managed therapeutic approach. The choice of management is correlated to many factors: gestational age, underlying pathophysiology of the arrhythmia, fetal heart rate, duration of the tachyarrhythmia, and presence or absence of cardiac dysfunction. A large review of fetal arrhythmias was been reported in our work.