The circulatory system may be divided into:

1. The pulmonary circulation where the right side of the heart circulates deoxygenated blood, via the pulmonary artery, to the lungs. There it is oxygenated, and then returned to the left side of the heart via the pulmonary vein.
The pulmonary circulation is a low pressure system. Typically pulmonary artery pressure is 15-30 mm Hg.