Right atrium: Right atrium is the thin walled right upper chamber of the heart. It empties blood into the right ventricle (lower muscular chamber) through the tricuspid valve. Right atrium receives blood from the upper part of the body through superior vena cava and lower part of the body through the inferior vena cava. It also receives blood from the coronary vein – draining deoxygenated blood from the heart muscle. Right atrium receives all the deoxygenated blood from the body.