Fig. 1
From: The timing of umbilical cord clamping at birth: physiological considerations
A schematic of both the fetal and newborn/adult circulations, showing the anatomical relationships, and connections (in the fetus), between the pulmonary and systemic circulations. Before birth, the majority of venous return to the left heart is derived from the placenta, which passes through the ductus venosus and foramen ovale, because pulmonary blood flow is low. After birth, following clamping of the umbilical cord, the supply of preload for the left heart switches from the placenta to the pulmonary circulation