Patients with untreated and severe congenital heart disease (CHD) rarely survive to reproductive age. A PubMed search revealed only 1 case of single atrium and single ventricle (SA/SV) in a pregnant woman; the patient was 6 weeks pregnant when dilation and evacuation was carried out [1]. The present case involved a primigravida at 32 weeks of pregnancy with untreated SA/SV who underwent successful operative delivery. It is reported not only because of its rarity but also to draw attention to medication use and unexpected reactions to conventional drugs. Informed consent was obtained for the present report. A 20-year-old woman with a history of complicated CHD was referred to the Second Affiliated Hospital of Xi′an Jiaotong University, Xi′ an, China, following irregular uterine contractions for 12 hours. The patient’s disorder was classified as New York Heart Association functional class III. Her vital signs were recorded as follows: temperature, 36.7 °C; heart rate, 90 beats per minute; blood pressure, 130/86 mm Hg; respiratory rate, 22 breaths per minute. Oxygen saturation varied between 80% and 90%. In addition, the patient exhibited cyanosis and grade 4/6 systolic murmur. Fetal ultrasound revealed the following parameters: biparietal diameter, 7.6 cm; femur length, 5.0 cm; amniotic fluid index, 10.0 cm; and placentalmaturity, grade 1. Echocardiography showed SA/SV, transposition of large arteries, and pulmonary valve stenosis (PS) in the mother (Fig. 1). A 5-g bolus of the tocolytic agent magnesium sulfate (MgSO4) was intravenously infused for 10 minutes. However, this infusion was stopped because the patient experienced chest tightness and shortness of breath. Patellar reflex was present and a low-maintenance dosage (1.5 g per hour for 10 hours) of intravenous MgSO4 was continued, leading to a clinical response. Five days after admission, regular uterine contractions were occurring every 2 minutes and cervical changes proceeded despite MgSO4. The patient requested cesarean delivery; under continuous epidural anesthesia, a premature female was born (1-minute Apgar score of 9). Uterine atony increased after 30 minutes, so oxytocin (0.02 IU/min) was intravenously infused and the patient’s uterus was continuously massaged. The preterm neonate (birth weight 1345 g) experienced pulmonary hemorrhage 2 days later and died. The patient was discharged 4 days after delivery and was stable at 6-month follow-up. Patients with untreated SA/SV rarely survive until adulthood. A previous study showed that pulmonary hypertension is a major problem during pregnancy among women with CHD [2]. The present case was rare because SA/SV was accompanied by moderate PS. Echocardiography revealed that the pressure gradient was 80 mm Hg and the maximumvelocity across the pulmonary valve reached 4.48 m/s. Single atrium and single ventricle without PS results in significant left-to-right shunt and pulmonary congestion, thereby progressing to pulmonary hypertension in a short period. In the present case, moderate stenosis of the pulmonary valve resulted in a brief left-to-right shunt and pulmonary congestion. Medication should be selected and administered carefully to reduce the effect on hemodynamics. Dose-related cardiovascular effects of oxytocinmay compromisehigh-risk patients [3]. Themost appropriate concentration of oxytocin not associated with severe adverse effects in patients with complex CHD remains unknown. In the present case, no evident cardiovascular adverse effects were detected during the continuous intravenous administration of oxytocin (0.02 IU/min) for 4 hours. The use of MgSO4 is controversial because a bolus dose may cause discomfort. As a calcium-channel blocker, MgSO4 elicits dose-related adverse effects on vascular smooth muscle and is associated with some cardiovascular symptomatology [4]. In conclusion, pregnant women with complex CHD may experience complications, so medication should be administered with care.