2001;121:798–803 Pharmacologic Intervention in the Fetus Edgar Jaeggi, Mike Seed Abstract With the arrival of echocardiography and magnetic resonance imaging, providing the means of noninvasively detecting and monitoring anomalies occurring during pregnancy, the fetus with congenital heart disease has increasingly become the target of prenatal treatment Nonetheless, pregnancy is a unique situation, as treatment of the fetus cannot be approached independently from the concomitant treatment of the mother, especially when a medication is used for indications other than those listed in the drug monograph This includes the off-label administration of pharmaceutical agents via the maternal circulation or directly into the fetus to treat tachyarrhythmias, cardiac inflammation, and/or congestive heart failure and to promote lung maturation Other interventions, such as the supplementary maternal inhalation of oxygen, may be useful to promote the growth of underdeveloped left heart structures and improve oxygen delivery to the fetal brain―for example, in cases of congenital heart disease or with intrauterine growth restriction due to placental failure This chapter discusses the rationale and outcomes of fetal pharmacotherapy for selected cardiovascular indications, with the caveat that controlled studies on drug efficacy and drug safety as well as universally accepted recommendations to guide prenatal treatment are largely unavailable Keywords Fetal; Pregnancy; Treatment; Pharmacotherapy; Antiarrhythmic therapy; Steroids; Hyperoxygenation