In which department does the heart begin, the big circle?

The systemic circulation begins in the left ventricle of the heart and ends in the right atrium. From the left ventricle, oxygen-rich blood enters the aorta – the main and largest artery in our body. Already from it, the blood enters all the other arteries, and through them saturates organs and tissues with oxygen, and also delivers various substances to them, and at the same time “takes” carbon dioxide and metabolic products, so that then through the superior and inferior vena cava to enter the right atrium … From the atrium, blood enters the right ventricle, where the small circle begins.