Where does the systemic circulation begin?

The circulation is a closed vascular pathway that allows blood to move through the body to transport oxygen, carbon dioxide, and metabolic products.
There are two circles: large and small. The large one begins in the left ventricle and returns to the right atrium. Arterial blood containing oxygen (shown in red in the figures) from the left ventricle enters all vessels of the body, supplying the cells with oxygen, but taking carbon dioxide and waste products from them. Such blood is called venous (blue in the figures).