The superior and inferior vena cava.
aorta
Blood that comes in to the right atrium comes from the pulmonary vein.
blood first enters the heart through the right atrium.
Veins, specifically the vena cava, enters the right atrium of the heart.
The blood enters through the superior and inferior vena cava.
The right atrium is where deoxygenated blood enters the heart.
Inferior vena cava
Veins return blood to the heart. Four veins enter the heart. The superior vena cava (SVC) returns blood from the head, neck and arms and enters the right atrium of the heart. The inferior vena cava (IVC) returns blood from the rest of the body and also enters the right atrium of the heart. The left and right pulmonary veins return blood from the lungs and enter the left atrium.
Oxygen-poor blood enters the heart through the right atrium
left ventricle Blood enters the left & right atria. Blood entering the left ventricle came from the left atrium. Blood from the body enters the right atrium. From there it is pumped to the right ventricle, through the lungs, to the left atrium, to the left ventricle, then throughout the body. Then back to the right atrium...
right ventricle then on to the pulmonary circulation, to the left atrium, left ventricle then to the body systems back to the right atrium.
Right atrium
Right atrium