A 2-month-old infant with gastroesophageal reflux was treated with cisapride. Bradycardia developed and an electrocardiogram revealed 2:1 atrioventricular conduction and a prolonged QT interval. After cessation of cisapride therapy, both the rhythm and the QT interval returned to normal. Prolonged QT interval during treatment with cisapride may occur in children as in adults.