Fetal tachyarrhythmias.

Fetal tachyarrhythmias are uncommon but are associated with significant perinatal mortality and morbidity. Fetal echocardiography permits the accurate determination of the nature of the arrhythmia. Transplacental or direct fetal therapy with anti-arrhythmic drugs can successfully cardiovert the fetus in utero with a subsequent reduction in perinatal problems. The investigation and management of these unusual conditions is reviewed.