Right Atria -The atria is the chamber in the heart where blood enters. The walls of the atrium are very thing to allow blood to return to the heart. The atria is the two upper chambers of the heart. The right atrium gets deoxygenated blood from the superior vena cava, inferior vena cava, anterior cardiac veins, and the small cardiac veins. The right atrium and ventricle are referred to as the 'right heart'.