RIGHT ATRIUM

• 60% of blood in the IVC is directed towards foramen ovale and the LA
• Blood from the SVC mixes with the remaining blood from the IVC and is directed through the tricuspid valve and enters the pulmonary artery via the RV outflow tract.
• During RA contraction.
• Foramen ovale flap and Crista dividens meet.
• Flow in IVC ceases.
• Flow in ductus venosus is forward even during atrial contraction.

The above changes increase the proportion of oxygenated blood in the proximal IVC. This arrangement allows foramen ovale to be continually flooded with abundant oxygenated blood. Overflow blood spills into the RA resulting in improved oxygen saturation in the RA.

Normal Right Atrium
Chiari network in right atrium
	Several linear structures may be present within the RA. Multiple linear echoes are unusual but can represent the Chiari network. This occurs when the resorptive process of the embryonic right valve of the sinus venosus leaves a fenestrated network of fibers. Although it has no clinical significance it has been reported in a fetus with premature atrial and ventricular contractions.