Valves in the veins prevent retrograde blood flow. The superior vena cava returns blood from the body area above the diaphragm. The inferior vena cava returns blood from the body below the diaphragm. The coronary sinus drains blood from the heart. Systemic and Coronary Circulation.
Pulmonary circulation begins with the right heart.
It is here that the oxygenated blood from the venous system enters the right atrium through two large veins, the superior and inferior vena cava. Blood is transported to the lungs via the pulmonary artery and its branches. Oxygen rich blood returns to the left atrium through cerebral pulmonary veins. With systemic circulation blood is pumped out of the left ventricle through the aorta and major branches to supply all of the body tissues. Coronary circulation, on the other hand, supply is the heart with its own network of vessels.