Progressive fetal atrioventricular block in heterotaxy syndrome.

We report a fetus with left isomerism, in whom the atrioventricular block progressed from low grade second degree to complete block and fetal hydrops. While it is known that there is a high incidence of heart block in the fetus with left isomerism, as far as we are aware, ours is the first report of Wenckebach type block documented in the fetus by Doppler echocardiography, and demonstration of the progression of heart block during fetus life in the setting of left isomerism.