Although great strides have been made in diagnosing fetal cardiac anatomic and functional abnormalities, in utero cardiac therapy is limited to the treatment of significant arrhythmias. The fetal prognosis may change if the dysrhythmia persists or if the condition results in intrauterine heart failure. When either complication is evident, intrauterine drug therapy may be indicated if the fetus is considered too immature for delivery. Information from case reports has shown several drugs to be useful to cardiovert the fetus, with digitalis being the pharmacologic agent used most often. At present, treatment consists mainly of transplacental administration of antiarrhythmic agents with the object of normalizing FHR and rhythm and abolishing, or preventing, fetal cardiac failure. Various agents have been used with variable success. More direct fetal therapy by intramuscular injection or umbilical vein infusion may replace unsuccessful indirect maternal therapy. It is unclear why some fetuses respond (or appear to respond) and others have hydrops and die in the absence of congenital heart disease or documented infection. With proper therapy, many fetuses survive and have a satisfactory prognosis, depending on the form of arrhythmia and the nature of any cardiac structural defects.