The paper is a review of cardiac arrhythmias, as the most common cardiological symptom in the fetus. After exposing the basic knowledge of fetal pathophysiology necessary for the better und understanding of cardiac rhythm disturbances in the fetus, the classification of fetal arrhythmias is presented. The possibilities of modern diagnosis and differential diagnosis, such us the fetal ECG, the control of the heart rate patterns and the sonography are discussed. The usefulness of the real-time-directed and color-coded M-Mode-echocardiography in the diagnosis and classification of arrhythmias are emphasized as well as the significance of the intracardiac Doppler and simultaneous Doppler recordings in the inferior vena cava and aorta. The indications, ways and drugs used in the intrauterine therapy of arrhythmias are presented. The differentiated management related to the diagnosis is described, after reporting about our own experience with 261 fetuses with arrhythmias (27 tachycardias, 21 bradycardias and 213 ectopic beats).