The ventricle of a functionally univentricular heart is known to be dilated, hypertrophic and hypocontractile before and after completion of a Fontan type of circuit. Ventricular dysfunction can be due to the congenital malformation itself, previous surgical conditions, or the very abnormal working conditions of the ventricle at the various stages of palliation. Because of the very different types of ventricle, it remains difficult to assess size, shape, hypertrophy, stress, strain, contraction and relaxation. The ventricle after birth tries to adapt to different and very abnormal circulations, evolving from overloaded and overstretched while shunted, to underloaded and overgrown after a Fontan type of circulation.