Humans show double circulation. This includes two circuits: pulmonary and systemic. Pulmonary means blood from the heart enters the lungs and then back to the heart. It includes the right ventricle, lungs, and left auricle. Systemic circulation is blood from the heart enters the body systems and then back to the heart. The blood from the left ventricle enters the body through the aorta and this is oxygenated blood. The blood then returns back to the right auricle and this is deoxygenated blood.