Fetal echocardiography now affords an accurate clinical diagnosis of nonimmune fetal hydrops secondary to fetal tachyarrhythmias and/or certain types of congenital heart disease. Individual case reports of the treatment of tachyarrhythmias have been reported that use various drugs, including digoxin, propranolol hydrochloride, procainamide hydrochloride, and digoxin plus verapamil hydrochloride. We found no report of intrauterine treatment of congestive heart failure due to congenital heart disease with sinus rhythm. The seven cases presented herein include five cases of isolated supraventricular tachycardia, one with supraventricular tachycardia and myocardial tumors, and one of congenital heart disease with congestive heart failure. Maternal treatment with digoxin converted tachyarrhythmia to sinus rhythm in all six fetuses, and resolved the hydrops in the fetus with congenital heart disease. Premature delivery was avoided in five of the seven cases with favorable outcome in six of the cases. In five mothers who were given oral digitalization, the fetuses had delayed (three to 35 days) response to therapy. Two mothers were treated intravenously and the fetus responded to therapy in less than 24 hours. Because of problems possibly related to poor absorption and/or rapid clearance of digoxin, the intravenous route of administration should be used as the best way to achieve adequate therapeutic levels in the fetus.