Yes it is a Blood Vessel
The vena cava carries deoxygenated blood into the left atrium.
pulmonary veins
The Pulmonary Vein carries oxygenated blood from the lungs to the Left Atrium.
The pulmonary veins bring oxygenated blood from the lungs to the left atrium of the heart.
Blood that comes in to the right atrium comes from the pulmonary vein.
Right atrium and Left atrium
vena cava
There isn't one. The pulmonary artery flows from the lungs to the Left atrium, to the left ventricle, and then to the aorta
the size of the right atrium is smaller that the left atrium.
The left atrium empties into the left ventricle. The left atrium and left ventricle are separated by the left AV valve, or mitral valve.
Right Atrium , Left Atrium , Right Ventricle , Left Ventricle