A female fetus was diagnosed at 30 weeks with a type of heart failure called hydrops fetalis, and she had a heart rate of 300 bpm. The baby was delivered by cesarean section at that time, because of the obstetrician?s concern for the baby?s safety. Because of marked edema with this type of heart failure, however, it was very difficult to intubate her. An echocardiogram later showed minimal heart contractions, so we were reluctant to give her intravenous antiarrhythmic drugs. We instead inserted an esophageal lead connected to a stimulator that, when necessary, delivered two or three paced beats to terminate the tachycardia. This worked well for about 24 hours, until incessant tachycardia developed. As soon as we stopped pacing the tachycardia, it would begin again. The tachycardia wasn?t originating with premature atrial contractions or single extra stimuli. Another mechanism, sinus acceleration, was involved with the tachycardia initiation. We then paced the baby?s atrium at a rate of 320 bpm, and the ventricular rate decreased to 160 bpm. We continued this for two or three days, stopping the pacing occasionally to see what would happen. Within a few minutes of pacing cessation, the tachycardia always recurred. Several days later, however, her heart failure had improved and, once again, we needed to pace only during tachycardia recurrence. After further improvement of her heart failure, she was managed with amiodarone for about nine months. She was one of the lucky infants who eventually outgrew her condition.