We describe two fetuses presenting with hydrops and tachycardia who were treated by prolonged dosage with procainamide. Initial therapy with digoxin in both had been unsuccessful in controlling the rapid heart rate. The first child was delivered after five weeks of transplacental therapy, and demonstrated Wolff-Parkinson-White syndrome on the second day which was controlled with flecainide. The second fetus required three and a half weeks of intrauterine treatment. Wolff-Parkinson-White syndrome became manifest four days after premature labor at 33 weeks gestation. No tachycardia occurred postnatally and the infant has been well during follow-up. The implications of treatment are discussed.
