Response of the fetal heart to charges in load: from hyperplasia to heart failure.

The article reports that the fetal circulation works in parallel with the dominant right ventricle, ejecting approximately 60% of the combined ventricular output. Three important communications exist between the two circulations (oval foramen and the arterial and venous ducts) that influence loading conditions. In particular, the determinants of fetal left ventricular filling differ considerably from those seen in the adult heart. Pulmonary venous return contributes only a small proportion to left ventricular preload because of the relatively low pulmonary blood flow in fetal life (rising from an estimated 11% to 25% of right ventricular output by the third trimester).