Summary: We present the case of a twin pregnancy in which 1 fetus developed hydrops secondary to supraventricular tachycardia at 30 weeks’ gestation. Transplacental flecainide administration successfully treated the condition without evidence of maternal or fetal side‐effects. The case raises ethical and possibly legal issues that present when 1 fetus in a twin pregnancy develops a condition the management of which could cause complications to the other twin and/or the mother.