A heart , or central motor organ. Through its rhythmic contractions, the heart ensures the movrment of blood in pulmonary circulation(right auricle-left ventricle) and systemic circulation (left ventricle-right auricle). After being oxygenated in the lungs, the blood from the veins is pumped into the aorta, the longest and most voluminous artery, from which it supplies the entire organism.