The illustration shows the ventricles of the heart and their blood supply. As the central circulatory organ, the heart fuels two series-connected circulation. The systemic circulation starts in the left ventricle of the heart, from where the high-oxygen blood is pumped into the aorta, then into arteries and arterioles, finally reaching the capillary bed. From there, the blood flows into the venoles and veins, to the inferior and superior vena cava, and finally to the right atrium of the heart.
The pulmonary circulation starts with the right ventricle of the heart, from where the desoxgenized blood is pumped to the lung capillaries via the pulmonary artery, from where it then returns to the left atrium via the pulmonary vein, so that the systemic circulation can start again. The atria are separated from the ventricles by atrioventricular valves, the ventricles and their efferent vessel are separated by the aortic or pulmonary valve.