Junctional ectopic tachycardia (JET) in infancy is one of the serious arrhythmias which can be fatal. Typical features of JET include rapid and irregular heart beats with atrioventricular dissociation. Two cases of JET are reported: Case 1 was a 35-week-gestational age newborn who was found to have hydropsy and fetal tachycardia at the 21st week of gestational age. Antiarrhythmic agents including digoxin, propranolol and verapamil were administered to his mother to treat the fetal arrhythmia without success. JET was recognized at birth which was spontaneously converted into a sinus rhythm at 1 month of age. The maternal history revealed that two previous pregnancies ended in hydrops fetalis, and one of these was documented to have fetal tachycardia. Case 2 was a 6-month-old male infant with JET and congestive heart failure. After failure of various antiarrhythmic agents, amiodarone finally slowed down his heart rate and controlled his congestive heart failure.