Background —Fetal tachycardia may cause hydrops fetalis and lead to fetal death. No unanimity of opinion exists regarding the optimum treatment. This study evaluates our experience with transplacental sotalol therapy to treat fetal tachycardias in terms of safety and efficacy. Methods and Results —The charts of 21 patients who were treated with sotalol for fetal tachycardia were reviewed. Ten fetuses had atrial flutter (AF), 10 had supraventricular tachycardia (SVT), and 1 had VT. Hydrops fetalis was present in 9 fetuses. Drug treatment was successful in establishing sinus rhythm in 8 of 10 fetuses with AF and in 6 of 10 fetuses with SVT. The mortality rate in this study was 19% (4 of 21 fetuses; 3 had SVT and 1 had AF); 3 deaths occurred just days after the initiation of sotalol therapy, and 1 occurred after a dosage increase. At birth, tachycardia was present in 6 infants. Two patients who converted to sinus rhythm in utero suffered from neurologic pathology postnatally. Conclusions —Fetal tachycardia is a serious condition in which treatment should be initiated, especially in the presence of hydrops fetalis. The high success rate in fetuses with AF suggests that sotalol should be considered a drug of first choice to treat fetal AF. The low conversion rate and the fact that 3 of the 4 deaths in this study occurred in fetuses with SVT indicate that the risks of sotalol therapy outweigh the benefits in this group and that sotalol should, therefore, be limited in the treatment of fetal SVT.