During the systole of the ventricle

During the systole of the ventricle the blood is pumped from the right ventricle into the pulmonary artery. When the right ventricle has pumped the venous blood into the pulmonary artery it enters the pulmonary circulation. The blood is brought to the lungs through the pulmonary artery. In the lungs the venous blood discharges out carbon dioxide. When the blood has discharged out carbon dioxide it takes in oxygen in the lungs.

The blood which has become oxygenated passes from the venous part of the pulmonary capillary system into the venules and veins. When the oxygenated blood has passed the four pulmonary veins it is brought to the left atrium of the heart.

Under the pressure in the left atrium the arterial blood which the pulmonary veins have brought to the heart is pumped into the left ventricle. During the prolonged contraction of the left ventricle, the so-called ventricular systole, the arterial blood is pumped into the aorta — the main artery of the vascular system. When the left ventricle has pumped the arterial blood into the aorta it is carried through the arteries to all the parts of the body.