Right Atrium: Entry Chamber for Systemic Venous Return

The right atrium receives deoxygenated blood from the systemic circulation via two great veins:

• Superior vena cava (SVC): Drains head, neck, upper limbs, upper thorax.
• Inferior vena cava (IVC): Drains abdomen, pelvis, lower limbs.

Blood then passes through the tricuspid valve into the right ventricle → pulmonary artery → lungs for oxygenation.

Key Anatomic Features

• Sinus venarum: Smooth-walled posterior portion (SVC/IVC entry).
• Pectinate muscles: Ridged anterior wall/appendage.
• Crista terminalis: Ridge separating the two.
• Fossa ovalis: Remnant of foramen ovale (fetal shunt).
• Coronary sinus: Drains cardiac venous blood (opens near IVC).
• SA node: Pacemaker at SVC-RA junction.

The right atrium is a low-pressure reservoir (mean pressure 2–6 mmHg) that facilitates venous return and atrial kick (20–30% of ventricular filling).