Various physiologic mechanisms have been proposed to account for the development of hypoplasia of the left heart. The mechanism thus far most widely accepted suggests that the entity starts as severe or critical aortic stenosis during fetal gestation. Obstruction at the level of the abnormal aortic valve is then held to increase left ventricular afterload, resulting in decreased systolic and diastolic function. Shunting across the patent oval foramen is then reversed, so that blood flows from left to right. This reversal of flow during fetal gestation decreases the volume of blood crossing the mitral valve, thus decreasing the further potential for growth of the left ventricle.1 Additional support for this postulated physiologic mechanism was provided with the advent of fetal echocardiography during the 1980s.2–4 It was the group of Allan, working at Guy's Hospital in London, which first documented the fetal development of hypoplasia of the left heart by serial echocardiographic observation.4 In their retrospective study of 7000 pregnancies, 462 fetuses were diagnosed to have a structural cardiac defect at the time of the initial echocardiogram. Among those, 28 patients had dilated and dysfunctional left ventricles and aortic valves. The majority of these patients were also found to have concomitant endocardial fibroelastosis. Out of 15 patients in the series who were followed with serial echocardiograms, five progressed to develop hypoplasia of the left heart. With echocardiographic technology undergoing refinement over the same period, it was during this era that the first fetal cardiac intervention was performed using echocardiographic guidance.2,5,6 With still further technologic advances, fetal diagnosis of hypoplasia of the left heart can now be made as early as 13 weeks gestational age.7 One entity which is frequently associated with the hypoplastic left ventricle and aortic stenosis is endocardial fibroelastosis. There is an overlap of pathology between these three entities.8–10 In this report, we describe our own experience in intervention in a fetus suspected of developing hypoplasia of the left heart.